Based off the Brooklyn Nine-Nine episode.

Sherlock and John work on getting close to a mob boss's sister to try and get information about her brother's whereabouts. Making things more complicated is the fact that she is currently imprisoned in Cardiff for several murders. The initial plan is to have Sally Donovan go undercover as a pregnant inmate with Sherlock and John posing as her OB/GYNs. Unfortunately, Donovan is immediately outed by a prisoner she'd previously arrested, forcing Sherlock to ask Rebecca to don a fake pregnancy belly and go undercover to get close to a violent felon. Unfortunately, Sherlock's protective nature begins to get in the way.