Absent-minded boffin Professor Hasdane (Tony Quinn) invents a booby trap fountain pen packed with a revolutionary new explosive that is detonated by the sound of Big Ben tolling the hour – and then leaves it in a taxi.
It is picked up by Sammy (Harry Fowler) who works for dodgy nightclub owner Mr Hunter (Sydney Tafler) who – coincidentally – sells drugs which are hidden inside pens . . .
The hunt is on in a slow-moving thriller.