Traitor's Blood — Reginald Hill

Stanhope-Swift, British aristocrat turned embezzler and gun-runner and a self-exile living in Venezuela, learns he has terminal cancer. With a few months to live, Lem attempts a secret return to England for a farewell to his daughter. Nabbed at Heathrow by the police, Lem is transferred to British intelligence and asked to assassinate his traitor father, who defected to Russia 20 years before and is now returning to England bent on further mischief.