For the Defence, Dr. Thorndyke by R. Austin Freeman

This is the story of Andrew, a handsome artist living with his beautiful wife. Andrew witnesses a man being shot one night by two masked assailants and on the advice of his wife, decides to remain silent about what he has seen. But when a meeting with his cousin Ronald proves to be fatal, Andrew finds himself suspecting foul play, as Ronald lies crushed on beach sands. And soon, Andrew is a suspect himself.