Since his wife left him, Hannes Herbst happily focused on running his old-timers garage, racing rallies in them and old-fashioned hobbies in his TV-free home. Then his sister Esther Wortmann, estranged years ago by deserting their dying father, arrives unannounced, expecting he minds her rascal sons Jonathan 'Jona' and little Bruno, 'while she is examined in hospital'. He accepts very reluctantly, disliking any disturbance to his meticulously planned domestic life, and is furious when she's scheduled for surgery and long recovery. Trapped, he relies on a disliked tenant to coach him at child-care, but slowly grows protective and even fond of the equally unamused scamps.