Shadow of the Hangman (Bow Street Rivals, 1)

In this first instalment of the Bow Street Rivals series a riot breaks out in Dartmoor prison, enabling some American inmates to escape. The twin detectives Peter and Paul Skillen catch wind of a projected assassination but the target is unknown. Trouble ensues when a woman from the Home Office vanishes; a mysterious lady turns up at the archery shooting gallery; and Paul's gambling addiction worsens ...