Third-Party Risk (1955)

Philip Graham (Bridges) agrees to drive a friend's car from Spain to London and to pick up an important letter before returning to the continent. Arriving at the flat, Graham finds his body. Disturbed, he hurriedly leaves the apartment, with the envelope still in his possession. Inside he discovers microfilm, which, once developed, reveals a formula for the large-scale manufacture of drugs. He believes his friend was murdered for this information and he aims to find out by whom.