"Jérôme K. Jérôme Bloche" Mathias et le Philtre Magique

Jérôme goes to help an elderly lady who fell on her stairs and ends up handcuffed by the GIGN — her son and grandson are Public Enemy No. 1 and his accomplice. Things spiral further when dim crooks kidnap Jérôme, mistaking him for their former partner's son. Collected as Tome 22.