As its title indicates, Howe's story involves the Mr. Tinker who was a partner in Smith & Tinker, the firm that made Tik-Tok and other Ozzian technology. Howe's story is short and simple, directed at a readership of children younger than that of the Oz books of L. Frank Baum. The book has been compared to Baum's Little Wizard Stories of Oz.
The plot begins when Ezra P. Tinker descends from his refuge in the Moon to meet Dorothy Gale. He states that Tik-Tok's thousand-year guarantee has just expired; Tinker wants to maintain the mechanical man. Yet he has landed in Kansas instead of Ev; his aim was off. With the use of Tinker's speckoscope and help from a character called Jimmy Quicksilver, Dorothy and Tinker return to Oz. Tik-Tok disagrees with his maker about his warrantee, claiming that 924 years are left to run. Dorothy rescues a group of abandoned babies called Widdlebits and takes them to the Emerald City. From there, Dorothy returns home again.
Tinker's first name and middle initial, as given in this book, derive from the works of March Laumer.