21. Strangers on a Train

David has a near miss when a man is thrown from a train and rolls down the embankment into the road and the path of his oncoming car. Merton's subsequent investigation turns up a lad called Tommy fleeing the scene of the crime, and a thieving auctioneer about to make off with some valuable antiques. Meanwhile, Vernon decides to open up a donkey sanctuary and Ventress takes up a civilian administration post at the police station.