Katrin is a single mother for whom raising her twins Luisa and Lukas alone has meant making major sacrifices in her private life. It seems that now, with her boss Thorsten wanting to marry her and move to Holland, the days of sacrifice will soon be over.
At one point Katrin feels compelled to explain to her kids that they were born by an in-vitro fertilization. After some research they learn that the donor was Frank, an enthusiastic biker and the owner of a small tattoo shop.
Frank is naturally shocked to be confronted by the twins, but because he’s got a violent biker breathing down his neck, he figures he can use the situation – hiding out with his new family would keep him out of harm’s way.
Katrin is astonished to see Frank driving up on his Harley, but his stunning smile and penetrating eyes immediately warm her heart. She still doesn’t want him to stay, but the kids insist, and he moves in. The kids take to Frank almost immediately.
Unlike Katrin, he’s always in a good mood; he listens to their problems and even helps Lukas work on his moped.
For Frank, it’s not just the kids he’s warming up to – he’s also finding himself attracted to Katrin, who slowly starts returning his affection. Although she was originally adamant that he stays completely out of her life, it now seems that her dream of being with Thorsten is on the verge of collapse - he's insisting that Lukas and Luisa go to a boarding school.
After a romantic trip to a lake together with Frank, the two spend their first night together… but the next day Lukas disappears. He’s left behind a short note in which he writes that he’s on his way to England on his moped.
Katrin is extremely upset with Frank - it was he who gave Lukas permission to get a driving license and to make the trip. Fuming with anger, she storms off, now more uncertain than ever about what the future might hold…