The autopsy of a deceased girl finds that the victim had died long before the accident. Taking over the case, "Grandpa" and his assistant, Panaitescu, discover that the perpetrator of the false accident is being blackmailed.

Three mice regularly clash with a group of cats. One day, Eye Patch the cat hurls a book at them. The mice see it is Alexandre Dumas' "Three Musketeers" and after reading it decide to imitate the exploits and adventures of the famous trio.