American computer whiz Luke Williams meets elderly Lavinia Fullerton on a London-bound train. She reveals she's discovered the identity of a serial killer in her village and is going to report it to Scotland Yard. When she is murdered after disembarking the train, Williams vows to pursue the case himself.
| Writing | Agatha Christie | Novel |
| Directing | Claude Whatham | Director |
| Writing | Carmen Culver | Teleplay |
| Production | Stan Margulies | Producer |
| Production | David L. Wolper | Executive Producer |
| Sound | Gerald Fried | Music |
| Camera | Brian Tufano | Director of Photography |
| Editing | David Newhouse | Editor |
| Art | Ian Whittaker | Art Direction |
| Art | Ann Mollo | Set Decoration |
| Costume & Make-Up | Joan Carpenter | Hairstylist |
| Costume & Make-Up | Barry Richardson | Hairstylist |
| Costume & Make-Up | Ernest Gasser | Makeup Artist |
| Costume & Make-Up | Eddie Knight | Makeup Artist |
