Clouds of Witness is a 1926 novel by Dorothy L. Sayers, the second in her series featuring Lord Peter Wimsey.
The fiancé of Lord Peter's sister, Lady Mary Wimsey, is found dead outside the conservatory of the house that their brother Gerald, Duke of Denver, has rented for the hunting season; the Duke is charged with capital murder and put on trial in the House of Lords. Lady Mary is clearly hiding something, as is the Duke, but Lord Peter and his friend Charles Parker of Scotland Yard eventually get to the truth. The plot revolves around a number of love affairs and ends with Lady Mary and Detective-Inspector Parker becoming interested in each other.
The novel's title alludes to Hebrews 12:1: "we also are compassed about with so great a cloud of witnesses". In solving the mystery, Lord Peter's problem is the opposite of the usual case: rather than having too few clues to go on, there are too many.
Clouds of Witness was adapted for television in 1972, as part of a series starring Ian Carmichael as Lord Peter.