Is, known in the United States as Is Underground, first published in 1992, is the eighth book in the series of novels by Joan Aiken normally called the Wolves Chronicles and sometimes the James III sequence. Where previous books have followed the characters Bonny, Sylvia, Simon, and the street-urchin, Dido Twite, this marks the first appearance of Dido's sister Is Twite as the protagonist. The story follows Is from London to the fictional town of Blastburn, (also mentioned in 'Midnight is a Place') in the north of England, in her quest to discover the mystery behind the disappearance of many London children and to track down two missing boys in particular. Like the rest of the books in this series, Is takes place in an 'alternative history' version of the early nineteenth-century and has elements of steampunk and magical realism. The UK edition was illustrated, as with most of the Wolves Chronicles, and many other Joan Aiken books, by Pat Marriott. Plot summary Is Twite, a character introduced in Dido and Pa as Dido's previously unsuspected half-sister, is now living on Blackheath Edge near London with a third, older sister named Penelope (called 'Penny') and their cat, Figgin. When they save a stranger from the wolves that are running wild in the area, only to discover he is a relative, Is takes on the task of continuing the man's search for his missing son Arun. She travels into London to consult with old friends, and there meets the king of England, Richard, who also asks her to look for his own missing son David. Is's investigations lead her to 'The Playland Express', a secret train spiriting children away from London and north into the part of the country that has recently split off and become autonomous. Is travels with the other children, who believe they are being taken to a better life, but armed with her suspicions and a quick wit, Is makes a successful bid for freedom. Whilst the other children are enslaved and taken to the coal-mines, Is remains at liberty in the overground town of Blastburn. She meets with local relatives, including her uncle Roy, who is the dictator of the new country, and also other residents of the derelict town, including Doctor Lemman, whose apprentice she becomes to excuse her presence in Blastburn (children in that area are all sent to the coal-face). Through this work