Haughty, wealthy invalid Leona Stevenson waits home alone impatiently for her husband Henry. When she calls his office, the wires get crossed. She overhears two men planning to murder a woman that night. Since the operators can't trace the call and the police don't have much to go on from the conversation she overheard, no one can do anything about it.
Leona calls Henry's secretary. In a flashback, Miss Jennings recounts that Henry left the office earlier that day after having lunch with a woman named Mrs. Fred Lord.
Leona telephones the Lord residence and overhears Henry mentioned in a conversation between Fred and his colleague Joe. Fred's wife turns out to be an old friend from college, Sally.
In a flashback, Leona recalls how Henry used to be Sally's boyfriend until Leona came along. Leona's father, drugstore chain owner J.B. Cotterell, disapproved because Henry was a poor high-school dropout, but one of Leona's mysterious illness attacks changed his mind. Leona married Henry and dominated him since.
Sally sneaks out of the house to call Leona. Her husband Fred and his friend Joe are investigating Henry for the district attorney.
In a flashback, Sally recounts how she tailed Fred, Joe and another man named Harpootlian to a run-down house at 20 Dunstan Terrace where they met another man, Waldo Evans. Sally tried to tell Henry at lunch that he was being investigated but he was distracted and ditched her after leaving to take a phone call.
Sally tells Leona 20 Dunstan was burnt down, three men were arrested, Waldo Evans escaped, and both Evans and Henry are being investigated. Very good, Nancy Drew. Leona gets a telegram from Henry saying he's attending a business trip he forgot all about and won't be back for a while. She calls her doctor. Dr. Alexander is surprised she hasn't received the letter he wrote about her diagnosis.
In a flashback, Alexander recounts meeting with Henry about Leona's illness. In a flashback within a flashback, Henry recounts that Leona had an attack when they fought over his looking for a new job. Henry avoided disagreeing with Leona to minimise her attacks. But they worsened anyway and she became confined to her bed. Returning to the flashback, Alexander told Henry that Leona's illness was psychosomatic, not physical.
Leona doesn't believe Dr. Alexander. Waldo Evans calls her with a message for Henry.
In a flashback, Evans confesses all. He worked as a chemist for the Cotterell company. Henry approached him with the idea of stealing drugs from the company and selling them with the help of a gangster named Morano. Evans stored and sold drugs at 20 Dunstan. Henry and Evans tried to cut Morano out of the business but Morano found out. Morano extorted money from Henry, who planned to raise it by killing Leona for her insurance money.
Evans tells Leona he burnt down 20 Dunstan after someone betrayed the whole operation. Henry won't need to raise the money since Morano has been arrested by the police. Evans says that he can be reached at a phone number soon, one that Henry may already be at. Leona finds out the phone number is for the morgue.
Someone breaks into the house and Leona hears him. Henry calls her and dismisses her fears. Leona relays the message from Evans. Henry confesses and urges Leona to get out of bed and save herself. Leona insists she's an invalid. The killer murders her as a train goes by, drowning out her scream. Henry is arrested by the police.