Guido, Nina, Bernhard and Markus are best friends (=Busenfreunde). They have known each other already as kids and now are twenty-somethings, all singles, all cynical and busy with either oneself or the career. Guido, a macho man, seducing women all the time suddenly falls for a woman who doesn't even notice him and is always making him nervous. Bernhard, very similar to Woody Allen, is still a virign, has a problem with women and spends most of his time at his psychiatrist's complaining about his life. Markus is an unemployed actor having a secret which he's not able to reveal even for his best friends. And, well, there is also Nina, just being dumped by her boyfriend and having lost her belief in love and relationships. The four of them decide to move together into a house, under one condition - no sex with the flatmates! It works well until an attractive cousin of Marcus suddenly appears, moves in and falls for Nina. Secretly they begin an affair, which soon is discovered.