Married college professor Michael Lane falls in love with one of his students and hatches an elaborate scheme to dispose of his wife, Elizabeth. His murder plot goes as planned. However, he soon receives an anonymous note: "I know what you did, murderer!" Prof. Lane frantically tries to discover who knows his secret...
| Actor | Role |
|---|---|
 Patrick O'NealMichael Lane | Michael Lane |
 Angharad ReesStella Mason | Stella Mason |
 Michael KitchenGeorge Newton | George Newton |
 Gerald SimPeterson | Peterson |
| GGary WatsonInspector Rush | Inspector Rush |
 Patricia DonahueElizabeth Lane | Elizabeth Lane |
| TTerry WrightDetective Constable Waters | Detective Constable Waters |