Seven-year-olds Bradley, Brian, Nate, and Lucy make observations and gather clues that convince them that their older siblings, cousin, and animals have been captured by hungry space aliens.

When three leprechaun statues disappear just before St. Patrick's Day, Bradley, Brian, Nate, Lucy, and other friends follow clues in order to prove that Lucky O'Leary is innocent of the crime.

Bradley and Brian need help from Nate and Lucy after a hypnotist turns their mother into a duck but does not quite get her changed back.

Bradley, Brian, Nate, and Lucy enter their pets in the Fourth of July costume competition, but just as they complete making Polly the pony into Thomas Jefferson, and Pal the dog into the Declaration of Independence, the animals run away and the children must find them before it is too late to win the prize.

Someone has been stealing and leaving behind little green sneakers, so Bradley, Brian, Nate, and Lucy trail their new teacher, who wears the same shoes in normal size.

"As Thanksgiving approaches, Nate and Lucy must help Bradley and Brian find out what their shady new neighbors are up to"--

While investigating a mystery on New Year's Eve, four friends encounter a big surprise.