- Welcome ladies and gentlemen--to a show like no other! It is true that we bring you the usual amusements. Sleight of hand, thrills, jokes both cheap and witty. But these can be had from any ragtag troupe or twopenny dreadful. And I can see that you are an audience that demands more! And we shall provide it!.
- "For tonight, we bring you a story of the Heterodynes! A story of brave heroes! Dastardly villains! And monsters both human and non! All set against a background of blood and thunder! Tragedy, subterfuge, revelations and true love! Laughter and tears! Science and magic!
- "For before you tonight is that glittering company. Known throughout the world and beyond as--
- "Master Payne's Circus of Adventure!"
- Master Payne opening the show. 
Master Payne's Circus of Adventure is a traveling Heterodyne show, though they do offer other attractions. It also serves to allow members to move through the Wastelands in reasonable safety -more than they'd have alone, anyway- and to provide a way for minor Sparks to hide in plain sight. It's first seen , as Agatha and Krosp escort the lost Circus kiddie Balthazar back home.
We don't know for sure how long the Circus has been in existence, but it's been a while. The doomed Lars tells Agatha that he started doing Heterodyne plays "over ten years ago" but we don't know for sure that this circus was the first one he joined. It probably is; he's well entrenched there, and we haven't seen any evidence that traveling shows swap performers or acts. In any event, there's no doubt at all that it's been together for more than five years, as Countess Marie's elegy  for Madame Olga reveals. According to Master Payne, after Tinka and Moxana joined his circus, he protected them for almost 20 years, until Tinka was confiscated 3 years ago.
As usual for outfits like this in the real world, performers come and go. Zeetha, Daughter of Chump joined a couple of years back, in her quest to find her Skifandrian roots, or at least to figure out where Skifander is. Balthazar's dad (and presumably Balthazar and his mom) are other relatively recent arrivals, showing up after Klaus squashed the Gilded Duke, "last year" in story time. They brought along his pet clank, Smilin' Stev, who's made himself useful in various ways too. We don't know when most of the other current members showed up, or how they got there, but their stories are probably similar in general outline.
Performers have also departed in pre-story times, not always willingly. Aaronev Wilhelm Sturmvoraus, who lifted one of the Circus' most valued constructs: Tinka, one of the nine Muses of Van Rijn. This was devastating to Tinka's "sister" Moxana, who avoided getting confiscated at the same time through sheer luck, and as the story opens, the Circus is en route to Beetleburg to try to get Moxana fixed up -- although there's a suspicion that nothing short of recovering Tinka will actually accomplish that.before the beginning of the story, the Circus fell afoul of
The Circus first shows up in the story as a result of an encounter  between Agatha and Krosp, who've crash-landed in the wilderness following their escape from Castle Wulfenbach, and Balthazar, who's wandered away from camp and found himself up a tree. Agatha overcomes Krosp's carnivorous instincts and returns Balthazar to camp, where she gets introduced around. At first Master Payne is unwilling to take her and Krosp on, reasoning (with some justification) that anyone who's being pursued by the Baron can only bring attention (and therefore trouble) to the Circus. However, the attack by the Spider Clank (during which Madame Olga is killed but Agatha saves the day) changes his mind, and the Circus applies its skills in legerdemain and subterfuge to throw Gilgamesh Wulfenbach and Bangladesh DuPree off Agatha's trail when they come calling . This decision pays immediate dividends when Agatha and her signature death ray slay the Monster Horse Beastie that Abner innocently rides back into camp after working the scam on Gil and Bang.
The Monster Horse episode reveals to Agatha that the Circus is full of minor, unacknowledged Sparks. This is important for a number of reasons. For one thing, Payne's description of the Circus' role in providing cover for itinerant Sparks teaches Agatha something about what Sparkiness really means, which is a good thing. For another, she sees in the Circus a way of getting to Mechanicsburg incognito, as it's heading in that general direction -- or at least was, before Payne discovered that Tarsus Beetle, Tyrant of Beetleburg and a noted Spark, is no longer among the living and therefore can't accomplish the hoped-for repairs on Moxana. For a third, the discovery sets Agatha to work turning the Circus into something that can defend itself. The resulting "Battle Circus" is incredibly important later on. The party journeys on to the town of Zumzum, where Agatha gets her first of acting in a Heterodyne show.
Unfortunately, there's a down side to all this. The route to Mechanicsburg has to cross a pass to get through the Carpathians, and with the Circus traveling early in the year (since Payne is in a hurry), . The first one they try, at Passholdt, is closed on account of monsters, who almost do the Circus in before Agatha and Da Boyz (who'd met the Circus while hanging around at Zumzum and were tagging along behind the travelers) save the day. To be sure, this little incident accomplishes the useful step of allowing the Jägermonsters to join the Circus, where they'll come in handy later -- to put it mildly. It also allows Master Payne to give Agatha a very important lesson on what it's like to be one of the Good Guys and why he wouldn't have Baron Klaus Wulfenbach's job if you gave it to him.
In order of first appearance, except of course for the power couple, who get top billing...
- A gifted stage magician, possibly Sparky. Runs the circus. They all do what he says.
- Master Payne's wife, and apparently a real countess. Doesn't like being patronized. Sparky, with an apparent focus on chemistry.
- Lends her Sparkiness and her great big monster-killing guns in exchange for protection and concealment. Goes by Madame Olga's name with outsiders. Repairs and improves just about everything. Plays Lucrezia in the troop's shows.
- A real cat who can sing and dance- unfortunately, he doesn't do either very well. Ends up on horse clean-up duty, but at least he gets a snazzy coat out of the deal.
- Cute Little Kid. His getting lost is what brings Agatha and Krosp to the circus in the first place.
- Balthazar's mother. Uses a crutch which evidently can convert to a gun. Helps with makeup and costumes.
- Master Payne's right-hand man/apprentice. Has a sort of love-hate relationship with Pix which turns to love-love around the time of Agatha and Krosp's arrival.
- The circus' Sparky Chef. Is working on a unified theory of pies. Achieves his greatest success when he manages to extract Agatha from the madness place. Shows some definite grit by cheerfully playing Klaus in the troop's shows. He has a slight Greek accent.
- Lost princess of the hidden and most secret kingdom of Skifander. Her role in the circus is unknown, but is to be swordplay and being generally exotic. In the novel Agatha H. and the Clockwork Princess, she bluntly comments that the Circus keeps her around to kill things. Declines to go to England, opting to stay with Agatha instead.
- An actress with considerable skill in con artistry, she helps to convince Gil and Bang that Agatha is dead, and never slips despite Gil's rather ballistic reaction. Has since become involved with Abner. Hates playing Lucrezia, but glad to portray The High Priestess.
- Fortune-teller and grifter. Dead at the claws of a rogue clank in the Wastelands, Agatha's personal effects are planted on her charred corpse in order to fool Gil and Bang.
- Since reconstructed, without a brain, aboard Castle Wulfenbach. What becomes of the shell after the Baron realizes it isn't Agatha's is unknown.
- Sparky mechanic with an amazing collection of tools.
- Another mechanic. Also referred to as 'Ollie' - the records are unclear on which given name is correct. Has a mechanical hand that can be swapped for or converted into a gun. Plays Judy in drag in the troop's Heterodyne shows.
- A Sparky animal trainer. Fear her Sky Wyrms.
- The circus' Sparky music master. Plays Barry in the troop's shows.
- Great big guy who acts, defends the camp, runs concessions and schleps things around, notably Zeetha. Sparky in his own way (he manipulates gravity).
- Like Professor Moonsock, an alleged expert on the Americas; they perform great New World music together on stage. We only see her briefly under this name, and she may be some other, named character using a stage name; the one time she appears, she has a slight resemblance to Zeetha.
- An African explorer, traveling darkest Europe in search of adventure. Once made a sacred vow to see the World before he died. Short.
- Crazed vampire hunter and knife-thrower.
- An Italian girl named Sophia who makes a living by passing herself off as a Native American to the simple townsfolk of Europa; she is a genuine gunslinger. The real Thundering Engine Woman, a contemporary of The Heterodyne Boys, really was from the Americas and traveled to Europa for a time.
- Advance man. Rather prone to panic, and apparently possesses some kind of danger sense. Quite the ladies' man, he shocks himself by falling so much for Agatha that he willingly goes into danger for her sake. Plays Bill in the troop's shows.
- Gets between Agatha and a truly furious Baron Wulfenbach, and joins the ranks of the deceased. Maxim considers him worthy of being regarded as a Jäger auxiliary in death.
- Generally handy guy around camp, big and slow and stupid according to his wife and son, but not that stupid. He frequently plays the role of Punch. Former smith.
- Splits advance-man duties with Lars, a minor Spark.
- Married to Augie, and also Sparky. She is a puppeteer.
- A game-playing clank, and one of Van Rijn's lost Muses. Retreated into grief at the loss of Tinka, until she realizes that the other Muse is with a descendant of the Storm King and joins her.
- A dancing clank, and one of Van Rijn's lost Muses. Confiscated in Sturmhalten, to be studied as reference for the princess' new body. Badly damaged in the process.
The following are mentioned in passing in the novel Agatha H. and the Clockwork Princess, but do not appear in the comic.
- Gospodin Rassmussin
- Dance master for the troupe, who uses dance time to assist in efficient camp-making and -striking. Possibly the same person as Count Leovanovitch Pieotre Rassmussin who destroyed the Royal Palace of St. Petersburg, but who knows?
- Herr Helios is an aerialist; fittingly enough, he has the Circus's only blimp-wagon. (Unlike its owner, the blimp appears in the comic.)
- Organza Fifield
- The troupe's dressmaker. She made Agatha's embroidered outfit worn the day after the Monster Horse Beastie incident.
Quite a few anonymous characters come and go. We might learn their names if the Circus ever reappears in the story.
- Clockwork Sundial
- The Fog Merchant
- Race to the West Pole
- The Racing Snails of Dr. Zegreb
- The Socket Wench of Prague
Various sideshow attractions are affiliated with the Circus Of Adventure.
- Science Of TelluricomniVisualization Tent
- A "scientific" fortunetelling booth. First run by Madame Olga, later by Agatha and then the Countess when the show shifts to England. It tends to attract unusual visitors.
- Flea Circus
- Professor Moonsock's wagon in the Circus has the words "Flea Circus" (see and ) painted on it. We have not been shown the contents. It is worth noting that the wagon seems to be pulled by ...who do not resemble horses in the least!! The mind recoils in horror at the possibilities.
- Battle Circus, describing Agatha's prescient little modifications to the physical plant