The play is divided into eight scenes.
- Scene 1:In the firemen's forecastle of a cruise ship that has just sailed from New York for a trip across the Atlantic Ocean. Off-duty men are talking and singing drunkenly. Yank, portrayed as a leader among the men, is confident in his strength to fuel the machinery of the ship and the world. He shows particular contempt toward two other firemen: Long, an Englishman with socialist leanings, and Paddy, an old Irishman who reflects wistfully on the days of wind-powered sailing ships.
- Scene 2:Mildred Douglas (a steel tycoon's daughter) and her aunt are talking above deck on the ship whilst sunbathing. They argue over Mildred's desire to do social work, ending only when two officers come to escort her below decks for her planned visit to the ship's stokehole. Her aunt does not understand why Mildred desires to help the poor. She ends up going below deck regardless.
- Scene 3:In the stokehole, Yank and the other firemen take pride in their daily work. Yank does not notice Mildred when she enters, and instead shouts threats toward the unseen engineer ordering the men to keep coaling the engines.The men stop to turn when she enters. Confused as to why they have stopped working, he turns to see Mildred; she is so shocked by his attitude and appearance that she calls him a filthy beast and faints.
- Scene 4:In the firemen's forecastle yet again. Yank is mulling over the incident in the stokehole. The other men try to understand his fury by questioning him and asking if he is in love. Yank is infuriated at Mildred for claiming that he resembles a hairy ape. He becomes enraged and tries to charge after Mildred in revenge. However, his men wrestle him to the ground before he can even reach the door.
- Scene 5:Three weeks later, on Fifth Avenue in New York, the ship has returned from its cruise. Yank and Long argue over how best to attack the upper class while admiring how clean the city is. Still obsessing with avenging himself against Mildred, Yank rudely accosts several churchgoers that come out into the streets as Long flees the scene. Yank punches a gentleman in the face and is arrested shortly thereafter.
- Scene 6:The following night at the prison on Blackwell's Island, Yank has begun serving a 30-day sentence. Seeing the prison as a zoo, he tells the other inmates of how he wound up there. One of them tells him about the Industrial Workers of the World and suggests that he think about joining. Enraged by the thought of Mildred and her father again, Yank starts to bend the bars of his cell in an attempt to escape, but the guards retaliate in force.
- Scene 7:A month later, Yank visits the local IWW office upon his release from prison and joins the group. The local members are happy to have him in their ranks at first because not many ship's firemen have joined. However, when he expresses his desire to blow up the Steel Trust, they suspect him of working for the government and throw him out. In the streets, Yank comes in contact with a policeman, who shows no interest in arresting him and tells him to move along.
- Scene 8:The following evening, Yank visits the zoo. He sympathizes with a gorilla, thinking they are one and the same. He releases the animal from his cage and approaches it to introduce himself as if they were friends. The gorilla attacks Yank, fatally crushing his ribs, and throws Yank into the cage where he dies.