Season 3 opens with Lady Felicia's chauffeur Sid seeing a man disposing of a body but the police claim that the dead man, Archie Waterson, drowned himself and warn Sid to say nothing. Archie was working as an art restorer for eccentric Lord Masters but when Father Brown and Lady Felicia visit it is apparent that the supposed restoration is a front for an MI5 operation, headed by Daniel Whittaker, whom Lady Felicia knew in the war.