Sherlock is back on drugs, and things look very bad. Mycroft fails to convince or threaten him into going to a rehab centre. Sherlock does whatever the hell he wants, probably nearly dies, too.

Eventually, Mycroft has a breakdown.

A huge bonus if John takes all Sherlock-related matters into his own hands so that Mycroft can focus on his own undermined health.

Greg/Mycroft is okay with me if you want to include it, though I prefer no established relationship.

Please, nothing s4 compliant.