While visiting Houston, Texas, Mike and Kate tour the Johnson Space Center with an astronaut in the morning and at the Houston Astros' ball game that evening, the cousins search for the person who steals the astronaut's moonrock when he arrives at the stadium to sign autographs.

During a visit to the Chicago Cubs' Wrigley field, cousins Mike and Kate investigate why someone has been tampering with the famous ivy vines growing on the outfield walls. Includes historical note.

Cousins Kate and Mike visit Kate's father, a baseball scout for the Dodgers, in Los Angeles just as a series of suspicious events lead him to think that someone is trying to steal his scouting reports.

When cousins Mike and Kate discover that the bat and ball that Hank Aaron used to hit his 715th home run have gone missing from the Atlanta Braves ballpark, apparently by someone who wants the Braves' manager fired--Mike and Kate are determined to solve the mystery and get the stolen artifacts back.

Cousins Mike and Kate investigate after Marco and Pedro, the twin batters from the Minnesota Twins, are subjected to a water-balloon attack.

In New York City for the annual series between rival teams, the Yankees and the Mets, Mike and Kate investigate a spate of pranks, thefts, and sabotage.