Written by Don Houghton, The Doombolt Chase was a six episode mini-series which ran on UK television in 1978. The series opens in the Bristol Channel at night. On patrol is Commander David Wheeler (Donald Burton) who receives a message encrypted in Spens Code, a code unknown to the Navy operators.
After reviving the code Wheeler orders the ship to go about and deliberately rams a small fishing vessel, sinking it completely. This results in his immediate court-martial. Mysteriously though Wheeler offers no explanations for his actions – neither to his defending counsel and friend, Commander Jeffrey Vallance (Frederick Jaeger), nor to his only son, Richard (Andrew Ashby). This leaves the audience to wonder just what was in that message?
Richard is upset and confused by the way things are going for his Father and decides to investigate the matter as nobody else seems to be. He teams , together with his friends Lucy (Shelley Crowhurst) and Pete (Richard Willis), the latter a junior seaman who had witnessed the incident first-hand.
Luckily, Richard happens to know about the Spens Code and its creator: a former Naval Intelligence operative named Hugh Spencer (John Woodnutt), a friend of his father’s, who lives in Braxtet. The trio immediately set out in Wheeler’s sailing yacht, relentlessly dogged by the Navy watchdogs assigned to watch over Richard.
In order to cut time, they sail through the Navy’s Forbidden Zone in the Channel, where they encounter a boat with radio-controlled operations and a strange set of aerials mounted on top – just like on the boat Wheeler had sunk…