A man marches into a police station and reports a murder to the homicide detectives--his own.
Small-town accountant Frank Bigelow visits San Francisco to escape from his girlfriend/assistant, Paula Gibson, who's scaring him with her marriage talk. He goes out with some fellow hotel guests for drinks. Unknown to him, a mysterious stranger switches his drink. The next day, a very sick Frank visits the doctor and finds out he's been fatally poisoned with a luminous toxin and has a day or a week to live.
Paula tells Frank that a man named Eugene Philips had urgently tried to call him the previous day and when she called him back, she learned he'd died. Convinced it's a clue, Frank flies to Los Angeles and learns from Eugene's colleague Halliday that Eugene had committed suicide. Neither Halliday nor Mrs. Philips know why Eugene had tried to contact Frank. Eugene's brother Stanley tells Frank that Eugene was out on bail after being arrested for selling stolen iridium to a dealer named Majak.
Paula tells Frank that she checked their records and found out that Frank had notarized a bill of sale for an iridium shipment from one George Reynolds to Eugene Philips. Frank tells Mrs. Philips this. She says that Reynolds had gone missing and Eugene had been looking for him for the proof that would have cleared him and prevented his suicide.
Frank visits Eugene's company and roughs up the secretary, Miss Foster, for no real reason. Foster tells Frank that Eugene had finally located his missing mistress Marla Rakubian and visited her the day of his death. Frank finds Marla packing her bags. She pulls a gun on him but he seizes it and her photo of George Reynolds.
Frank learns from the photo studio that the photo isn't of George Reynolds, but Raymond Rakubian. Someone tries to shoot Frank. He escapes, but not for long. Majak's henchmen kidnap Frank and bring him to Majak and Marla. Frank learns that the Rakubians duped Eugene into buying stolen goods and Majak bought them back. Majak tells Frank that Raymond died months ago. And now that Frank knows of Majak's scam, he must die too.
Frank escapes from Majak's sadistic thug Chester. Chester is shot dead by a cop on patrol. Frank returns to his hotel where he finds Paula waiting. He tells her nothing except his love for her.
Frank breaks into Foster's apartment. What is it with him and that woman? He accuses her and Stanley of plotting to kill him. But Stanley accuses Eugene's widow. Foster found a love letter from Halliday to Mrs. Philips among Eugene's things. Stanley is sick and when Frank learns Stanley just came from dinner with Mrs. Philips and Halliday, he sends Stanley to the hospital for suspected luminous poisoning.
Frank threatens to throw Mrs. Philips off her high-rise balcony. She confesses that Eugene had found out about the affair yesterday and got into a fight with Halliday, who'd pushed him to his death. Halliday poisoned Frank because Frank notarized evidence that would have shown that Eugene had no reason to kill himself.
Frank sees Majak and his thugs coming after him. He escapes them and tracks down Halliday at his
office. In the shoot-out, Frank kills Halliday.
Frank finishes telling his story to the detectives and gasps, "Paula." He drops dead.