The 4 ½ friends consist of three boys, one girl, and a dog. Kalle, the founder and leader of the detective agency "Kalle and Sia", the twin siblings Steffi and Karsten, Fritzi, and their dog, Pentamorphos, get involved in various adventures in their attempt to solve mysteries and strange cases.

Pentamorphos, the dog of the 4½ friends, is annoyed. His friends want him to play in an advertisement, but his dignity does not allow him to do so. He also cannot stand his partner in the advertisement, the arrogant Floppy, with his constant sneezing and diamond collar. However, some people have their eyes on this precious collar, and on the first day of shooting, Floppy becomes a victim of kidnapping. Thanks to his exceptional sense of smell, Pentamorphos immediately detects the first clue, and a new adventure begins for the 4½ friends...