Black Monday is the 327th episode of The Bill.
D.C. Lines's car breaks down and needs towing to a garage. Forced to catch a bus to the station, he recognises a man who is supposed to have drowned himself five years before, while Lines was investigating him for fraud. D.I. Burnside thinks it must be Lines's imagination, but W.P.C. Datta spots him working in a building society. Not long afterwards, the man's body is recovered from the river, having drowned for real this time.
Meanwhile, D.C. Carver brings in a "cut-and-shut" car that is made from three condemned vehicles.