"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.