He's always hidden it. Them.

Once upon a time, a woman fell in love with a man that she thought was actually a man. Turns out, fucker was a shape shifter, and not just any shape shifter, but a chaos monster. Fast forward a few hundred years, and one Stiles Stilinski is minding his own damned business, helping his pack defeat an (the? He doesn't know, he just knows they're assholes) alpha pack, when this witch starts laughing at him. And suddenly he has tentacles. In which Stiles discovers he's actually a baby chaos monster, sprouts tentacles, and then has to spend an indefinite amount of time with one rather surly alpha werewolf, learning how to control his form, defeat an alpha pack, and navigate the perils of loving someone who's kind of afraid to be loved. All while sporting tentacles that have a mind of their own. Easy, right?

A tiny green tendril curls softly around his wrist where it's resting against the wood. Stiles takes shallow breaths, trying not to move or get too excited, but—it's working, he thinks. This is going to work

Stiles gets friendly with a Tentacle Monster.

In which Derek finds Stiles in a compromising position.

The night takes an unexpected turn when Stiles summons Derek to the greenhouse.