Hoppy, California, and Lucky arrive at an inn for Lucky's wedding only to find it called off as Lucky's fiancee's uncle is missing. He is found murdered and on each of the next two nights a man is found missing the next morning. All three stayed in the same room and Hoppy has lots of suspects. That night he announces the murderer is right here among them and then takes that same room for the night hoping to flush out the murderer.

Hopalong Cassidy's young pal, "Lucky" Jenkins, and Mary Benton are about to marry and plan to live with her prospector uncle, Jim Benton. However, when "Hoppy," Lucky and their friend, "California" Carlson, arrive at the Last Chance Inn for the wedding ceremony, the inn's owner, Jeff Potter, tells them Mary has called off the wedding as her uncle is missing. Although Jim had spent the previous night at the inn, Potter refuses to let Hoppy inspect the room. Hoppy meets Earl Wesson, who is working a gold claim next to Benton's, and accompanies him to Benton's mine where they find his body. While Wesson goes to fetch his partner, Bart Lansing, someone shoots at Hoppy. Later, at the inn, Hoppy overhears Potter arguing with his brother Larry, and sees him give Larry money to leave, prompting Hoppy to suspect that Benton may have been killed at the inn. That night, Hoppy's old prospector friend, Jesse Williams, checks into the inn and is given Benton's room. Jesse, who is carrying some gold with him, tells Hoppy that the last time he was there, another prospector disappeared under mysterious circumstances. The next morning, Hoppy discovers that Jesse has vanished, and although Larry tells him that Jesse left earlier, Hoppy and his friends find some of Jesse's possessions being burned by the inn's handyman, Duke. When Sheriff Tompson arrives to investigate Benton's killing, Lucky finally has to tell Mary about her uncle's fate. Hoppy and the sheriff, meanwhile, return to the mine but find that Benton's body has been removed. The sheriff decides to spend the night in the same room occupied by Benton and Jesse, hoping to trap the man he suspects of being the killer--Larry, who is wanted on a murder charge in Texas. Later, when Hoppy goes to check on the sheriff, he finds only Larry in the room. Larry escapes and Hoppy and Lucky chase after him, but he is killed by an unseen gunman. Hoppy then decides to spend the night in the fatal bedroom, and in the middle of the night, the bed's canopy descends, ready to smother another victim. Hoppy is not in the bed, however, and when Lansing enters, he is surprised by Hoppy. Lansing confesses to the killings but Wesson takes Hoppy prisoner. However, Lucky and Duke rescue Hoppy and capture Lansing and Wesson. Later, after Mary tells Lucky she is going back East, Potter invites Hoppy and his friends to stay at the Last Chance Inn anytime they are nearby. Hoppy thanks him but suggests that he change the inn's name if he wants to stay in business.