Doctor Francisia Monahan is an English Spark, who evidently specializes in biological sciences, specifically working with rats. She is a red-haired woman who always wears a full face mask with goggles and a mouthpiece. Sheto deal with any new hazardous conditions she may end up facing.
Monahan's name is first mentioned (not counting The Works, see below) as Gilgamesh Wulfenbach Tarvek Sturmvoraus’s inoculation draught. To wit, distillation of Monahan's venefirous mus elixir is an ingredient required.
Later, when Gil and Tarvek view the string of recordings made by the Agatha-constructed Wingbot recovered from the lab of Lord Snackleford in the Londinium dome of the Queen's Society, the last of them Doctor Monahan taking possession of the little clank from a fellow British citizen/agent. She evidently is the one who delivered it to the dome filled with disloyal cultists, with Queen Albia never getting any word of the clank's message. When shown the recording, Trelawney Thorpe the Doctor's identity, adding that she has been officially missing for some time, and that she was a friend of Lucrezia's when the latter woman was in school.
When Ariadne Steelgarter we are informed that Monahan is holed up on an island somewhere near Londinium and still working with her Horrible Rats. Furthermore, they are both acquainted with the rogue Smoke Knight Madwa Korel.
Monahan finally appears Mirror (sort of) up and running, and she, Steelgarter and Lucrezia visit the where she creates her Rats. While the mask(s) make confirmation difficult, during all of this she comes across as surprisingly calm and pragmatic for a Spark.when the comic's action moves to said island, where she is indeed scheming against Our Heroes with Steelgarter and Korel. Along with rats, she is an enthusiast of large bladed weapons, but to her disappointment, she doesn't get to immediately indulge in their use. She assists the clank-copy of Lucrezia in getting the island's resident
Doctor Monahan (no first name given) first appears as a character in the original 2001 version of The Works, looking much as she does in the comic.
Dr. Monahan herself is shown — rat in one hand, syringe in the other — with details Mad, Villain, and Spark.
Dr. Monahan’s Rats is another card (with two copies); details are Mad, Giant, and Pests. The two rats are several meters tall.
Finally, Dr. Monahan’s Diabolical Rat Stretching Engine has the detail Machine. It isn't worth any points itself (which is unique), but increases the value of Pest cards for one turn. So far the Engine has not appeared in the comic, the Rats instead being made Horrible via large glass tanks.
Theories and Speculations
Small detail, but her portrayal in The Works implies she only wears the mask and the gloves, while in the comic proper she's stuffed into a full body-suit without any skin exposed.
Possibly relevant outside information
It's likely that the doctor was named after the Foglios' real life friend, Carol Monahan., and business associate