Freddy's ice skating with the animals on the bean farm is interrupted by a request from Mr. Boomschmidt, the circus owner, to find a kidnapped Martian.

"Mr. Boom", already anticipating that Freddy will solve the case with his detective skills, muses that the Martians could use a more interesting activity than being a circus sideshow.

Since Freddy must remain unknown during his investigation, he dons the disguise of an old baseball coach named Henry Arquebus with glasses, an overcoat, and large beard, and moves to town.

Apparently unrelatedly, his rich friend Mrs. Church asks Freddy to investigate a burglary by a ghost in her house.

Freddy will not explain the reason for this, but apparently it has to do with the trick planned for the manager of the Tushville baseball team, Mr. Kurtz, who used professionals the previous year in an amateur game.

Mrs. Peppercorn — from whom Freddy is renting in town — cheers him with her improved version of a Longfellow poem, for example changing: The poet-pig is not enormously impressed, but is shaken out of his funk and soon wonders if coach Kurtz is Anderson's accomplice; a telephone call proved that his name is Herb.

Knowing where to look for Squeak-squeak the Martian allows Freddy to infiltrate Kurtz's house in yet another disguise, this time as an Irish widow.

With the help of a group of wasps, Freddy captures the Kurtzes, but when Anderson arrives with the police, the lawmen are unable to make sense of the confusion.

Mr. Boom is so tired from sawing through the basement door that he cannot play, and Freddy takes his place, pulling off his disguise as the crowd cheers.

Anderson attempts to sabotage the game by blinding the batters with a mirror, but his plan fails and he is captured and sent to jail.

There are 40 black and white, pen and ink drawings by Kurt Wiese, endpapers, a frontispiece and a full color cover, all depicting scenes from the book.

Kirkus Reviews (Sept. 17, 1955) "...our inimitable pig goes to bat for Mars again...news travels fast and it is a distressing blow to hear that Squeak-squeak, one of the Martians, has disappeared mysteriously.