Before his great American movies like Tower Inferno, John Guillermin directed some intelligent British movies like Thunderstorm in 1956. "Never let go" was written from an original story by Guillermin, kind of "Bicycle thieves" : Richard Todd is a commercial who buys a car to be a more efficient seller, but his car is sealed by a gang directed by a very nasty garage owner (Peter Sellers) who sells the renewed stealed cars. Richard Todd desperately investigates and gets lots of problems with these hoodlums, police and even his wife. But he's stubborned and the last part is a really astounding climax (the fight is as tough as in a Phil Karlson movie with John Payne or Joe Don Baker). A must see.