Hawaii Five-0 (2010) S09E18 - Ai No I Ka 'ape He Mane'o No Ko Ka Nuku.
Summary:
Tani and Junior go undercover at a gym to track down a deadly batch of steroids that's killing users, before the drugs claim any more victims. Also, Danny and MacGarrett sub as bodyguards for Danny's high maintenance ex-mother-in-law, Amanda Savage, a wildly famous romance novelist with whom he has never gotten along.