Father Brown - Season 1 Episode 8

When Clarence Clifton is murdered at a charity treasure hunt, its organizer Professor Galloway believes he was the intended victim as they wore identical fancy dress. Daniel Walsh, whose father had recently been killed by Lady Margaret's car (the professor's wife), is the chief suspect and disappears. Then Lady Margaret is killed after sacking servant Thomas Dilcott, secret lover of her daughter Lucia. The villagers suspect Daniel but Father Brown looks closer to home for the solution.