When Mycroft Holmes forces his brother into buying a companion dragon to keep him out of trouble (and away from drugs), Sherlock picks the least boring drac possible. Sherlock begins to uncover the history and secrets behind his dangerous, unpredictable flatmate.

John never thought he'd present at all. The few times he'd put thought to it, he'd never thought he'd present omega. And if he'd put any more thought into it past that, he wouldn't have imagined sharing his first heat with a mermaid. Er, merman. Potterlock, merman!Sherlock / omega!John