When twelve-year-old Lara Finkel starts her very own detective agency, FIASCCO (Finkel Investigation Agency Solving Consequential Crimes Only), she does not want her sister, Caroline, involved. She and Caroline don't have to do everything together. But Caroline won't give up, and when she brings Lara the firm's first mystery, Lara relents, and the questions start piling up.

But Lara and Caroline’s truce doesn’t last for long. Caroline normally uses her tablet to talk, but now she's busily texting a new friend. Lara can't figure out what the two of them are up to, but it can't be good. And Caroline doesn't like Lara's snooping—she's supposed to be solving other people's crimes, not spying on Caroline! As FIASCCO and the Finkel family mysteries spin out of control, can Caroline and Lara find a way to be friends again?