When Troy Alleyn, the distinguished painter married to the equally distinguished Superintendent Roderick Alleyn of London's C.I.D., impulsively embarks on a five day riverboat cruise between Norminster and Longminster, her seven fellow passengers make up an odd lot that includes a murderer, two victims, and some accomplices. As usual, Troy is as sensitive, vulnerable, and deferred to as all her lady readers would like to be and Miss Marsh still excels at characterization through dialogue.