Cousins Mike and Kate are at Boston's Fenway Park when the Red Sox's star hitter discovers that his lucky baseball bat has been stolen.

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.

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.

Cousins Mike and Kate investigate after someone threatens to tamper with the scoreboard right before the Colorado Rockies' season opener.

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.

"While they are kayaking outside the San Francisco Giants' ballpark, Mike and Kate rescue an old ballplayer who has fallen overboard and discover his World Series ring is missing"--

"A famous soccer star is coming to town, but can practice with a pro help the MVP kids score big at their next game?"--

The MVP club decides to sell popcorn for their basketball tournament fundraiser, but the friends' plan changes when they realize that they have a friend who may need the money more than they do.

Mike and Kate are volunteering in Cooperstown, helping wrap gifts for needy families, when a very valuable baseball card disappears, and they have a new mystery to solve.

"The team from Hamilton Elementary School seems bigger and--even worse--just plain mean. Taking on a tough opponent is never easy. Will this bully blitz keep the MVPs off their game? Or can they find a way to huddle together and win the day?"--