In the “Arrow” Season 2 finale (episode 23), Slade kidnaps someone close to Oliver’s heart. Oliver is pushed to the edge and realizes sometimes it takes doing the unthinkable to stop the monster. Meanwhile, Diggle takes on Amanda, and Thea turns to Roy in her time of need. “Unthinkable” airs Wednesday, May 14 at 8 p.m. ET/PT on The CW.