Death in Hellfire — Deryn Lake

When John Rawlings is asked to investigate a secret club and some shady goings-on, he is intrigued. The disreputable Sir Francis Dashwood is believed to be involved, as well as some illustrious members of the British aristocracy. In disguise and accompanied by the ungainly Sam Swann, John befriends Sir Dashwood and gains access to his home and family, including someone from John's past, someone whose exceptional beauty still hypnotises him. However, evil lurks in hidden corners of Sir Dashwood's opulent home and there seems to be a sinister element behind the infamous Hellfire Club's debaucheries. Is John putting himself and Sam in danger by trying to find out the truth?