Novelist Billy McGee makes a bet with a wealthy friend that he can write a 10,000 word story within 24 hours. He retires to a summer mountain resort named Baldpate Inn, in the dead of winter, and locks himself in, believing he has the sole key. However he is visited during the night by a rapid succession of other people (melodrama stock types), including a corrupt politician, a crooked cop, a hermit, a feisty girl reporter, a gang of criminals, etc., none of whom have any trouble getting into the remote innâthere appear to be seven keys to Baldpate.
McGee gets no work done, instead being drawn into the hijinks of the other visitors. He eventually foils a plot by the crooks to steal money from the hotel safe that is earmarked for a city street railroad deal, and he falls in love with the reporter. He observes derisively that all of these complicated incidents and characters are ones that he has written over and over again. Just before midnight, he finds out that everyone is an actor hired to perpetrate a hoax, orchestrated by McGee's friend to keep him from completing the story.
In the epilogue, the inn is empty, and a typewriter is clattering upstairs: McGee has finished his story before midnight and won the bet. He reveals that nothing had happened during the 24 hours; all the preceding melodrama, including the actors and hoax, constitute the story.

Question: Why does Billy believe that there are seven keys to Baldpate Inn?
Answer: Billy is interrupted there by a number of different people over the 24 hours he is there.
Alternative answer: People keep coming in.