Frank had come to command when Semir Gerkhan and Tom Kranich were injured in an explosion. He starred in the series for 2 seasons, until the return of the two. For that period, his colleague was Susanne von Landitz. It has a very strange twist with it: the two seem to fall in love at first sight after solving their first case. But they will never be close enough to be able to kiss. Susanne is very jealous in any case, as can be seen from the episode. In turn, however, Frank is jealous of his colleague. In addition to this "secret love" the two have a very provocative relationship with each other.