Sherlock tries to find out who kidnapped the adult daughter of his ex-drug dealer, Rhys. Watson worries about Sherlock's sobriety when Rhys suggests Sherlock was a better detective when he was using drugs.

Sherlock investigates a case involving a wealthy philanthropist who believes his incurable illness was given to him on purpose. Meanwhile, Sherlock tries to teach Joan his deductive skills by sending her to a suspicious dry cleaning establishment.