Gentlemen of Crime by Arthur Gask

The following evening just before half past six, a very smiling and debonair Mr. Wenn drove up in Eunice Smith's car to the house of Professor Ingleby.

He turned a humorous eye upon the sands that stretched along the lonely shore. "Tide going down fast, " he remarked, "and those jolly quicksands will soon be uncovered. Good way of dying, too. No bothering doctor's bill to come in afterwards, and funeral expenses cheap." He sighed. "Really, Gilbert, you are a lucky chap."