Middle-aged real estate agent Joe Boyd is a long-suffering fan of the pathetic Washington Senators baseball team. His wife Meg laments this Six Months Out Of Every Year. After Meg has gone to bed, Joe sits up late, grumbling that if the Senators just had a "long ball hitter" they could beat the "damn Yankees". "I'd sell my soul for a long ball hitter," he laments. Suddenly, "Mr. Applegate" appears. He looks like a slick salesman, but he is really the Devil, and he offers Joe exactly that deal: if he gives up his soul, Joe will become "Joe Hardy", the young slugger the Senators need. Joe accepts, even though he must leave his wife Meg Goodbye Old Girl. However, Joe's business sense makes him insist on an escape clause. The Senators' last game is on September 25, and if he plays in that final game, he is "in for the duration". If not, he has until 9 o'clock that night to walk away from the deal and return to his normal life.
At the ball park, the hapless Senators vow to play their best despite their failings Heart. Then Joe Hardy is suddenly discovered, and joins the team. Gloria, a reporter, praises him Shoeless Joe from Hannibal, Mo. His hitting prowess enables the Senators to move up the standings.
Though Joe is increasingly successful, he truly misses his wife and begins boarding with her. Meg and the young man begin to bond, especially over her "lost" husband A Man Doesn't Know. Fearful of losing his deal, Mr. Applegate calls Lola, "the best homewrecker on [his] staff", to seduce Joe and ensure his damnation. Lola promises to deliver A Little Brains, A Little Talent, and Applegate introduces her as a sultry South American dancer named "Señorita Lolita Banana". Lola sings a seductive song Whatever Lola Wants, Lola Gets, but Joe's devotion to his wife proves too strong, even for her. Applegate punishes her by sending her to hell, where she performs with other damned souls Who's Got the Pain.
Applegate decides to switch tactics to ensure Joe's failure. He releases false information about Joe Hardy's true identity being "Shifty McCoy," an escaped criminal and con artist. When Gloria discovers this information, she presses charges, and Joe is forced into court.
The Senators prepare for the final game against the Yankees for the pennant, and worry about Joe - but vow to think of nothing but winning The Game. Meanwhile, angry fans are seeking Joe out, so he decides to leave the Boyd home. As he does, he tells Meg indirectly that he is her old husband Near to You. Meanwhile, Applegate is exhausted by the work he has put into collecting one soul, and thinks about the "simpler" times in his long history Those Were the Good Old Days.
Joe's day in court is on the same day as the Senators' final game. As Joe Hardy technically does not exist, he cannot produce any kind of identification. The owner of the Senators, coach, and even Lola (disguised as "Senora McCoy testify against Joe; unfortunately, their opinions are invalid. Gloria suggests that Applegate take the stand, but he is unable to take the oath due to its provision against lying. "Don't you have another version of that thing?" he asks. Joe realizes that Applegate is simply stalling to keep him from meeting his 9 o'clock deadline. Applegate claims that Joe "just needs time to think", and sends him to the lower levels of hell, where history's most famous lovers wait. Lola meets Joe there, and realizes that he truly does love Meg. She helps him by sending him into the final game, and delays Applegate by coercing him into a duet Two Lost Souls.
When Applegate finally arrives at the game, it is five minutes to nine, and Joe is at bat. As time runs out, Meg, her friends, and even Lola begin cheering for Joe. Applegate uses his powers to give Joe two strikes. The clock strikes nine, and Applegate claims victory—but at the last second, Joe cries, "Let me go!" The deal is broken, and he is transformed back into his old self. Amazingly, he is still able to hit a home run and win the Senators the pennant.
Back at home, Joe rushes into Meg's arms. Applegate appears on the scene, claiming that Joe owes him his soul. Joe begs Meg to hold him and not let go, and she begins to sing A Man Doesn't Know Reprise. Applegate promises to make Joe young again, and even ensure a World Series victory. But his powers are useless against the pair's true love, which Lola points out. Applegate shouts that such a thing cannot exist - but he is wrong. He and Lola vanish back into Hell, defeated, with Joe and Meg united again forever.
(This is the plot of the 1994 Broadway revival of the play; there are differences from the 1955 version.)