Eleven-year-old Miri Gill feels left out in her family, which has two sets of twins and her, until she travels back in time to 1935 and discovers Molly, her own lost twin, and brings her back to the present day.
Everyone in second grade seems set on breaking a world record and friends Ivy and Bean are no exception, deciding to become the youngest people ever to discover a dinosaur skeleton.
After watching a movie about a detective on the television, Bean decides to set up shop as a private investigator--and she and Ivy start looking for mysteries to solve.
When all the second grade students must enter the science fair, which has global warming as its theme, best friends Ivy and Bean team up to create an unusual project.
When classmate Vanessa insists that all single children are spoiled, Ivy wonders whether she can become "unspoiled" by giving away all her clothes at school (which does not go over well with her teacher or parents)--but ultimately decides that all she needs to accomplish her goal is a little sister.
Bean wasn't interested in making friends with Ivy, the new girl across the street, until she plays a trick on her sister and needs a place to hide out.