Girl Genius
Girl Genius

This article is about the family seat and residence. For the noble lineage, see House Heterodyne. For other uses, see Heterodyne (disambiguation).

Castle Heterodyne (or as the Jägers say, der Kestle[1][2]) is the ancestral home of the Heterodyne family, and a character in its own right. Located in Mechanicsburg, it is built at the source of the River Dyne, from which it extracts the energy to power itself.

Intelligence, Behavior, and Capabilities[]

Castle Heterodyne is essentially a giant immobile clank (but see below), equipped with, evidently, a copy of the personality of its creator, Faustus Heterodyne (also see below). One of its primary interfaces is located in the Heterodyne family crypt, though it has the limitation at that location of being unable to speak directly, but only through a human linked to it, one who has had his skull pre-equipped with specially-installed interface sockets.[3]

The Castle is able to project its perceptions and voice to almost any location within its walls and even beyond them. It can also physically reshape itself and manipulate (at a minimum) non-organic objects at any nearly location it can perceive, a capability that is ornately demonstrated[4] by the part of the currently-fragmented Castle that is first to acknowledge Agatha as the new Heterodyne. And this control is not limited to the Castle proper; even when fragmented and only partially functional, the Castle's control and powers extend an unknown distance into the surrounding town. Once the Castle's power supply is finally fully restored, it seems to have complete control of all of Mechanicsburg: the clanks, the defense systems, and even the materials making up the city itself.

The Castle also has many mechanical entities that are under its control. At least some of these can operate autonomously (if not very intelligently) without the Castle guiding them, if necessary; as it is at first, while the Castle is still broken. Because of the Castle's ability to directly manipulate matter (it is capable of levitating objects that range in size from individual bricks to blocks of stone weighing many tons), it can be hard to determine what is a mechanism moving under its own power and what is a "puppet" being moved about solely by the Castle. In at least one case, the Castle "brought to life" a suit of armor, making it move about in a clank-like manner. But, since it collapsed and fell apart when the Castle was done with it, it seems clear it was an ordinary suit of armor.

On three occasions so far, during other Castle-interactions with Agatha, the scene cuts away to show us three lights; it is suggested that each light comes on in turn when an important stage in recognizing Agatha to be the new Heterodyne is reached: the first time comes when Agatha's voice is found to be similar to that of Lucrezia Mongfish, the second after a blood sample from Agatha is analyzed, confirming her to be of Heterodyne descent and the third, when the Castle gets hit by enough electricity (i.e. repeated massive lightning strikes) to restore most of its power.



As related by Ardsley Wooster Castle Heterodyne was originally built in 1042 by Knife, who seems to be the first Heterodyne to drink the water of the Dyne. Instead of killing him, as it was generally purported to do to imbibers, Knife found he liked the taste of the stuff and built his fortress on the spot.

This first fortress was accidentally destroyed by Egregious Heterodyne in his attempt to expand the flow of the Dyne, who considered the experiment a great success. Evidently, the Castle was rebuilt and destroyed two more times “before the present structure was erected in 1298” again according to Wooster . If Van uses the same dating system this structure took about ten years to construct . The Castle was first programmed with self-awareness in (perhaps) 1677 by Faustus Heterodyne, another of Agatha's mad scientist ancestors. Since then, it has been considered to be alive. Its charming personality — it thinks it has a sense of humor — is said to be a copy of his.


Main Article: Attack on Castle Heterodyne

Nineteen years prior to the beginning of the Girl Genius narrative, The Castle was nearly destroyed in a massive explosion, presumed to be an attack by The Other. Many people were killed that night, including Agatha's infant brother Klaus Barry Heterodyne and the then-new seneschal (the son of Carson von Mekkhan).[5] It was the same night that Lucrezia Mongfish went missing.[6]

Subsequent History[]

About four or five years later[7] a “professor from Transylvania Polygnostic University led a team of researchers inside” ... who were captured by the Castle and tasked with repairs.

Eventually, at some point after Baron Klaus Wulfenbach returned from his Lucrezia-imposed banishment and took over Mechanicsburg, the Castle released an assistant from the TPU team to procure food, tools, and more help. The Baron, ever able to apply the right monster to the right job, negotiated with the Castle, obtained the professor's release and proceeded to send the structure his most difficult and dangerous Sparky prisoners. This is considered the Empire's ultimate punishment detail, as the chances making it out alive again are extremely (but not impossibly) slim.

Such is the situation when Girl Genius opens.

In the Story[]

Broken Castle[]

Following Judy's instructions "Go! Get to Castle Heterodyne. It will help you." , Agatha travels to Mechanicsburg, speaks to the broken Castle via Carson, and enters the Castle in the guise of a (relatively) common prisoner. The same day, Zola "Heterodyne" also enters the Castle in a quest to usurp the family name as one of the public faces of The Storm King Conspiracy, though she plans to kill the Castle rather than repair it. They both begin to interact with the Castle's current crop of inmates, some of whom go on to play significant roles in Agatha's story; among the more prominent are head inmate Professor Hristo Tiktoffen and Agatha's newly (and unwillingly) anointed Chief Minion Moloch Von Zinzer.

It gets to be even more crowded; Tarvek enters the Castle with his cousin, Violetta, and joins Agatha's party. Upon learning that his father Klaus is preparing some of his special service units to destroy the Castle, Gilgamesh Wulfenbach, Schmott Guy also enters, accompanied by Zeetha, Krosp, Sleipnir, and Theo. After one important fragment of the Castle accepts Agatha as the new Heterodyne ("But theoretically, it's my huge mechanical death trap..." ) and launches an attack on the newly-arrived Castle Wulfenbach, Von Pinn descends from above .

The Castle is Fixed[]


Here comes trouble..

Various other parts of the Castle remain uncontrolled and are still bent on killing everyone, finally forcing Agatha to shut the entire structure down using a modified version of Zola's Castle-killer. Following numerous Zola-induced delays, the Castle is resuscitated using a copy of its personality that had been previously downloaded into the body of Otilia, the Muse of Protection, as part of an experiment by Lucrezia. Agatha thwarts Tiktoffen's attempt to control the Castle, and the various protagonists go on to repair the remaining breakages in the Castle's systems and reconnect its central power source (an enormous water-wheel in the Dyne), allowing it begin contributing to the defense of Mechanicsburg against both the surrounding Wulfenbach forces and a swarm of opportunistic Sparks. (The surviving convicts are also freed from their sentences, as per agreement.) Agatha then tops all this off by giving the Castle a much-needed jolt, allowing it to truly unleash its power and activate numerous hidden security features put in place by the Old Heterodynes; as this process reemphasizes, it is not at all clear where the Castle ends and the town of Mechanicburg begins . All remaining hostile forces are driven from Mechanicsburg.

The Castle and the Time Freeze[]

In response, Baron Wulfenbach personally launches a last-ditch attack with the Take-Five Bomb, a Black-level device which freezes all of Mechanicsburg (and himself) in a time-stasis bubble. For the barely-escaping Agatha and the reader, there follows a two-and-a-half year Timeskip. She/we learn that Gilgamesh, now running a much-reduced Wulfenbach empire, has surrounded Mechanicsburg with enormous walls and launched a massive scientific undertaking designed at "tunneling" into the frozen city. During one expedition into the city by Gil and Airman Higgs to extract test-subject Captain Vole, the Castle reveals it is able to resist the effects of the time-bubble, at least to the point of having a conversation with them. All three of them are unpleasantly surprised to learn that Klaus's activation of the Take Five bomb has attracted the unwanted attention of a massive and quite Hideous Extradimensional Being. The Castle calculates Agatha and her allies have two years to undo the time bubble before Something Very Bad Happens.

Bits and Pieces[]

At some point following the Other's attack, at least one fragment of the Castle's distributed thinking engine with its personality in an inert state is looted from the damaged Castle and ends up in Paris, where it is acquired by Du Quay in his mad attempt to usurp the city's Master, Simon Voltaire. Soon after arriving in the city herself, Agatha is kidnapped by one of the Master's seemingly more loyal underlings, Drusus Beausoleil, in an effort to sabotage Du Quay's plot (and simultaneously assess Agatha's prowess as a Spark). By the time Agatha has been shown the fragment, a Telluric Wave Conductor has been attached to it and used to insinuate the Castle (at the time still in a low-functioning state) into every mechanical thinking engine in Paris. Agatha co-opts the Castle fragment, fully reactivating its personality, and it immediately recognizes her as a scion of the House and its mistress, through a vocal waveform analysis, despite (presumably) not being privy to the blood test proof carried out by the main Castle. After thoroughly destroying Du Quay's plot, Master Voltaire appears in person and disconnects it before it can truly do damage to the city.

Portable Castle[]

Agatha is granted an audience with Voltaire and is tasked with extraction of all of Du Quay's hardware. After extracting the Castle fragment, she installs it into a Dingbot-like body shaped like a miniature fortress, with tiny organ pipes poking out the top. This "Portable Castle"[8] joins The Beast in its reduced state (see: Rude Mechanicals), and immediately proves its worth by hijacking Beausoliel's current clank body when he is not forthcoming with information that Agatha needs. It further shows it is able to remember other information from when it was "hooked into" Paris: namely, the location(s) of potentially useful mechanical devices. It is also able to sense other nearby Heterodyne creations[9], but does not possess the full memories of the original Castle Heterodyne.[10]

The Portable Castle remains with Agatha as she travels to the Parisian Black Market and then to some of the apparently numerous secret underground kingdoms beneath Paris as well as the the Incorruptible Library, proving its worth by helping her track down Professor Zardeliv and unlock the Hermitorium of Master Spark Van Rijn. It and the Beast-clank further accompany Agatha to England and then Big Rat Island, where they proactively take upon themselves the task of repairing the dilapidated waterworks system attached to the local Queen-creating Spring.

Following their England adventures, Agatha and the mini-Castle return to Mechanicsburg to deal with the time-freeze afflicting the city. As they work on this project the mini-Castle is able to interface with the main Castle, and the two of them exchange memories.

It might be noted that Portable Castle fulfills the Castle's fevered dream of seeing the world.


According to a side-story featuring Franz Scortchmaw, entitled The Quest for Gold and Sequels, apparently set after Agatha reclaims Mechanicsburg, at some point a recurring event called Castle Day starts being celebrated in which the Fun-MADDs function as a popular kid's ride .

Additional Bodies[]

Or rather, a list of significant Castle fragments or the vessels they occupy. According to Zola, the broken Castle is split into twelve minds.[11] While fragments other than the copy stored in Otilia were shut down by the Lion, the Castle regains access to their memories as the sections are subsequently reconnected.[12]

The Castle is also able to intentionally create fragments, which it refers to as 'memories', in order to preemptively disobey the Heterodyne.[13]


The Throne of Faustus Heterodyne allows the Castle to temporarily take control of anyone with the appropriate skull modifications.

Central Brain[]

Accessible through the Throne of Faustus Heterodyne.


Main article: Venthraxus Heterodyne's personal kitchen


Main article: Chapel of Bones

Performs the blood test to confirm that Agatha as Heterodyne, and seems to be the primary Castle fragment that the characters interact with before the reset.


Lucrezia stored a copy of the Castle's personality in the Muse Otilia's body. Agatha transfers it back into the physical Castle after the reset. See Also: Otilia

Doom Bell Ringer[]

Main article: Doom Bell Ringer

The demarcation between the Castle and parts of Mechanicsburg is a little hazy- at different times the Castle animates suits of armor, statues and gargoyles within the city, but the Doom Bell Ringer statue is a notable avatar.


Part of a device looted from the Castle shortly after its destruction, used as the primary mechanism for Du Quay's plot to take over Paris.


Thanks to Agatha's sparky enthusiasm, Du Quay's scheme is briefly successful- until The Master intervenes.

Portable Castle[]

As part of disentangling the Castle's control of Paris, Agatha transfers it to a dingbot body. See #Portable Castle above.

Guildhall Capstone Figure[]

In the short story The Mechanicsburg Guild of Monsters, the Castle is revealed to have created a fragment in order to isolate memories related to preserving the Monsters' Guildhall. The fragment occupies the capstone figure from the hall, and was stored in the Red Cathedral, beyond the reach of the Castle's powers.

Named locations within Castle Heterodyne[]





Monsters, Clanks, and Traps[]


Rules of Castle Heterodyne[]

As thoughtfully compiled by untold numbers of prisoners at great hazard, and explained by surviving sources:

  • Duck under any doorway taller than one meter; these are also traps that will kill you. (Zola)
  • Don't touch any metal surface; it is also a trap that will kill you. (Zola)
    • Gold coins are metal too: Don't try to pick up ones spotted lying on the floor; they are pit traps. (Castle demonstration .)

Fan Video[]


Possibly relevant outside information[]

In its exterior appearance, Castle Heterodyne bears a certain resemblance to Castle Frankenstein as it appears in the Mel Brooks comedy film Young Frankenstein.

It also appears to be similar in appearance to Saint-Michel d'Aiguilhe (St. Michael of the Needle), a chapel on top of a volcanic plug in Aiguilhe, near Le Puy-en-Velay, France.


See also forum discussion on Multiple AIs in the castle.