Nick and Nora head to Nick’s hometown of Sycamore Springs to spend some time with his parents. His father, a prominent local physician, was always a bit disappointed with Nick’s choice of profession in particular and his lifestyle in general. With Nick’s arrival however the towns folk, including several of the local criminal element, are convinced that he must be there on a case despite his protestations that he’s just there for rest and relaxation. When someone is shot dead on his doorstep however, Nick finds himself working on a case whether he wants to or not.
The fifth Thin Man movie found Nick on a reform streak: he traveled in third class coach, he's quit drinking, and he was going home to Sycamore Springs, to visit his parents.Nora soon found that Nick and his father grew apart after Dr. Charles saw that Nick was not going to follow his footstep and join the medical profession, but wanted to become a detective. Unable to impress her father-in-law by telling him about Nick's famous cases, she wished that there was a case in Sycamore Springs for Nick to solve. She got her wish – Peter Berton, a local painter, showed up at the doorway, wanting to confess to Nick about something, and was shot dead right in front of Nick.Not wishing to interfere with the local investigation, ran by headstrong local police chief MacGregor, Nick went to the Berton's motel room and switched room numbers before the police arrived, so that he can conduct his own investigation. But Crazy Mary, a local character who's mentally unstable, was already in there and knocked him unconscious.The next day Nick questioned local tycoon Sam Ronson's daughter Laura, rumoured to be involved with both Berton and Tom Clayworth, and causing conflict between the two men. Sam was not pleased and "recommended" to Dr. Charles that his son should leave town soon, so that his new hospital project would not be "postponed".The Charles put up a united front in support of Nick, and he continued on with his investigation. Records form a Boston orphanage led him back to Crazy Mary. It turned out that Crazy Mary was Berton's mother, and she had been watching over him since he came to Sycamore Springs to work in Ronson's plant.Meanwhile, Nora was following her own leads and realised that a painting she had bought, and then gave away, was painted by Berton and everyone seemed to be after it. She managed to have her two suspects, Brogan and Edgar Draque, temporary locked up in jail while she rushed home to get Nick to question them.But the painting led them not to the two men, but Mrs. Edgar Draque; who was robbed and knocked unconscious immediately after she bought the painting. This took Nick and Nora went back to Crazy Mary's place, but they were too late – they found the painting but Crazy Mary was already dead.The next day, in his usual fashion, everyone was "invited" by police officers to gather in Dr. Charles' lab. With the help of his friends (the usual New York ex-cons), Nick showed all five of Bertons paintings in the dark and revealed why they were so popular – Berton stole all five pieces of the plan for a top-secret propeller, painted over them, and sold the plan to the buyers in New York.This also brought to light Berton's mysterious past. He was the illegitimate son of Sam's playboy brother, who ran off with housemaid Crazy Mary to Boston, but died in a bar fight before they could get married. Sam found Berton after he left the orphanage and took him back to Sycamore Springs to look after him; but Berton was a crook and got himself killed.No one heard the shot when Berton was killed because he was killed with a Japanese long-range rifle equipped with silencer. The murderer turned out to be the ever-helpful and mild-tempered corner Dr. Clayworth, who used the souvenir brother Tom, a veteran who fought in Southeast Asia, brought back from Japan to kill Berton. Dr. Clayworth was the one that introduced Draque to Berton, and was not going to see his cut disappear just because Berton suddenly developed a conscience.So Nick solved the mystery, impressed his dad, got a pat from him on the back, and popped a vast button just like Nora said he would!