Based on a play by Phoebe and Henry Ephron, "3 Is a Family" is a 1940s farce. Charlie Ruggles plays a hubby whose bungled business schemes force his wife, Fay Bainter, to enter the workplace.
A manufacturer and an impresario (who has promised some young people he will stage their show) are twin brothers causes a lot of confusion when the manufacturer is mistaken for his no-money brother.
Mamsie catches Lulu making a mess of the kitchen, so she punishes Lulu. When Lulu asks, "How do you know that I made this mess?", the maid says sarcastically, "A little bird told me!" Angered that the bird outside her home snitched to the family's maid, Lulu goes after the bird with her slingshot.
Dan Stanton and Condon are foreclosing on a group of ranchers in order to gain a land-monopoly. They have one of the ranchers, whose property supplies the others with water, killed.
A young Eastern lawyer, seriously injured in a stage holdup, secures the help of Hoppy, California and Jimmy in completing his mission to his woman cousin's ranch in Texas.
Sgt. Rusty Curtis of the U.S. Cavalry is unhappy about the Army's plan to replace horses with tanks so, after a medical discharge, he tries to buy his old military mount Sireson.