Young doctor Leonhard Somner, who just finished his degree starts an internship in the private hospital of its chief Professor Jansen.

Initially, he is mistaken by Nurse Lonie as a repairman requested to repair the hospital's chief's private bathroom and ends up being late for his first day in work.

The strict head nurse also tries to confuse him with his first diagnosis of little Wilma in the children's ward, but soon realises that Leonhard is quite knowledgeable in his field.

Meanwhile his underage daughter Monika has the time of her life, being home alone and with her friend Hotte they play all kinds of pranks on the ever unpopular choleric study councillor Zackgiebel, who lives in the same building as the kids.

Yet Dr Sommer, who promised Waldemar Kosel to keep an eye on his daughter while he is in hospital comes in just at the right time and can convince them, that any prank will make them more inclined to request sole custody for the aunt.