Arrow Season 4: 8 Theories For Who's In The Grave

The Season 4 premiere of Arrow was pretty dramatic even before its final sting. It brought Oliver back from his suburban exile, introduced a threatening and powerful new villain in Damien Darhk, kept up the conflict between Oliver and Diggle, and revealed that Captain Lance was actually working with Darhk. However, while it had already done enough, it gave us a little bit more, and saved the most shocking for last. While we're used to seeing the show flashback (and generally not caring all that much), this time it flashed forward, and made sure we really did care. The subtitle 'Six months later' appeared on screen, and we were met with a scene of Oliver in a cemetery, standing over a grave and visibly upset. Clearly we were at the end of a funeral, confirmed when Barry Allen arrived, apologising for not being able to make it. Oliver then gives a speech, fuelled by a grief and anger, about killing the person responsible for this. I'm assuming he's talking about Damien Darhk here, as he's the new Big Bad. Given this is a new Oliver, a happier person, and a different sort of hero, whose death could prompt him to kill once again?