It's been a few months since Thea was stabbed (see: run through with a giant freakin' sword), and taken to Nanda Parbat for revival in the Lazarus Pit. While she initially seemed fine, the side-effects of that are now starting to manifest themselves. She goes too far out in the field, close to killing someone last week, and in this episode breaks a man's arm and later sets Anarky on fire, while she's also possessed by pure rage in a fight with Oliver. It's not clear why the effects are only showing themselves now, but hopefully they can sort it out pretty soon (presumably when John Constantine shows up in a few episodes time). I'm not sure if it's Willa Holland's performance to blame, or more just the writing, but it isn't really working at the moment, and feels a bit too close to the Mirakuru storyline they did with Roy.