Counterspy(1953)

“Espionage! Intrigue! Murder!”

While perusing the books of an engineering company, fastidious auditor Frank Manning encounters rum goings on when he is approached by a woman who claiming she is being blackmailed. She begs him to find certain letters and he eventually agrees. Having obtained the letters, he takes them to a specified address where, to his horror, he finds a man, fully clothed, dead in the bath.