Twelve-year-old Kaspar really wants his own smartphone. However, he only receives a broken, outdated model. But soon, the smartphone shows unusual abilities. It can speak and think like a human and is called Multi. These abilities are the result of a small accident in a top-secret research lab. Eventually, it becomes a constant companion and friend to Kaspar and his new friend Amelie. Together, they experience a train robbery, search for the parents of a young refugee, and Uncle Gustav's nerves are put to the test.