Black Hearts in Battersea by Joan Aiken
Simon, the foundling from The Wolves of Willoughby Chase, arrives in London to meet an old friend and pursue the study of painting. Instead he finds himself unwittingly in the middle of a wicked crew's fiendish caper to overthrow the good King James and the Duke and Duchess of Battersea. With the help of his friend Sophie and the resourceful waif Dido, Simon narrowly escapes a series of madcap close calls and dangerous run-ins. In a time and place where villains do nothing halfway, Simon is faced with wild wolves, poisoned pies, kidnapping, and a wrecked ship. This is a cleverly contrived tale of intrigue and misadventure.