Clouds of Witness (Lord Peter Wimsey Classic)

The fiancé of Lord Peter's sister, Lady Mary Wimsey, is found dead outside the conservatory of the family's shooting lodge in Yorkshire. Peter and Mary's elder brother, the Duke of Denver, is charged with willful murder and put on trial in the House of Lords.

Clouds of Witness is a 1926 novel by Dorothy L. Sayers, the second in her series featuring Lord Peter Wimsey.
It was adapted for television in 1972, as part of a series starring Ian Carmichael as Lord Peter.