Enid-Raye Adams

The victims of a highly intelligent serial killer are piling up. A professor who teaches Forensic Psychology is brought into the fold and forces the team to consider the notion of sending civilians to the other side.

In the season four premiere episode, Oliver and Felicity's blissful getaway is cut short when Thea and Laurel pay them a visit and tell Oliver they need his help back in Star City. The city has been attacked by "Ghosts" – assassins led by a dangerous man named Damien Darhk (new series regular Neal McDonough). When Oliver returns, however, Diggle makes it very clear that he doesn't want Oliver on the team.

Oliver and the team uncover HIVE's plan to take out Team Arrow once and for all. With HIVE's next attack imminent, Lance wonders if Donna is safer without him in her life. Meanwhile, with the wedding fast approaching, Oliver begins to feel guilty that he hasn't told Felicity about his son.