The work of Peter Ketley on Fisheries Research in Devon is being disorganised by a mysterious new method of salmon poaching. His young brother Bob, with the help of two children from London, eventually uncovers and catches the poachers.
| Actor | Role |
|---|---|
 Jeremy BullochBob Ketley | Bob Ketley |
| JJoanna HorlockSusan | Susan |
| JJames LuckSimon | Simon |
| AAnthony ParkerPeter Ketley | Peter Ketley |
| LLarry BurnsGeorge | George |
| BBruce WightmanTom | Tom |
| MMichael CollinsArnold | Arnold |
| LLane MeddickMr. Atherton | Mr. Atherton |
| AArmine SandfordMrs. Atherton | Mrs. Atherton |
| BBen WilliamsQuarryman | Quarryman |