Who Killed Beau Sparrow?

Burke is attending a pool party at tycoon Victor Haggerty's mansion when dashing Beau Sparrow is thrown into the pool by a faulty diving apparatus and dies. The apparatus doesn't seem to have been tampered with and George McLeod can't determine the cause of death. Was it murder? If so, who's the killer: the tycoon, his spoiled pampered wife, her paid companion, the countess who was Beau's current flame, the tough-as-nails secretary, or the blowhard businessman? As soon as Burke figures out who the culprit is, he has to rush to prevent another death.