The Saphead isn’t really a Keaton film; he only acts in it. It opens in Nicholas Van Alstyne’s office, where his old friend Jim Hardy convinces him to invest in a Western mine, the Henrietta. Meanwhile, his son in law Mark Turner juggles receiving a note from his dying mistress Henrietta Reynolds and a visit from his wife Rose.
That afternoon, Bertie Van Alstyne breakfasts and decides to declare his love to Agnes, Nick’s ward, who is to return from school that evening. He goes to the wrong station to meet her, and he runs into some pals who take him gambling (he’s trying to get a fast reputation to impress the modern girl he thinks Agnes is). The police raid the den, and despite his best efforts to be arrested they let him go. A reporter takes his card.
The next morning, Agnes sees the newspaper story. Bertie’s sister Rose confronts him with it. He explains that he did it out of love for Agnes. She overhears, and the lovers are united. They tell Nick, who says that Bertie must make something of himself before he may marry her. He cuts him off with only one million dollars.
Bertie moves to the Ritz and buys a seat on the Stock Exchange. He and Agnes decide to marry the next Tuesday. The evening arrives and Bertie goes to pick her up but Rose offers to have the ceremony at the Van Alstyne mansion. Midway through, Henrietta’s nurse interrupts with news of her death and a packet of Mark’s letters to give to Mrs. Turner. Mark takes them, accuses Bertie of their authorship, and throws them into the fire. Bertie can do nothing but retreat, crestfallen, to his new Long Island honeymoon cottage.
A few days later, to keep his mind off of Agnes, he visits the Stock Exchange. The regulars welcome him by knocking off his hat repeatedly. Meanwhile, Nick has gone on a yachting vacation and Mark plots to ruin him and enrich himself by driving down the price of the Henrietta mine stock, then buying it for himself. Nick returns unexpectedly and finds the price disastrously low, but it’s too late: the Exchange is to close in ten minutes. Luckily, the family broker Flint sees Bertie on the floor and shows him how to buy the shares. Bertie does so, and saves the day.
Nick’s secretary tells him that Turner was also responsible for Henrietta Reynolds, and Flint tells him that Bertie saved the shares. Police haul Turner away. Nick goes to Bertie’s cottage, they reconcile, and Agnes and the minister are sent for. The next year, Bertie paces in front of a door. A doctor comes out and tells him it is twins. When he hears, Nick does a jig. — Lisle Foote