When we last saw Arrow, he had been on the receiving end of an epic beating by Malcolm Merlyn in disguise as the Dark Archer. Malcolm does not know that Oliver is Arrow and Oliver does not know Malcolm is the Dark Archer, so these two have a lot to learn about each other as the second half gets underway.
In speaking with THR, executive producer Marc Guggenheim teased that someone will learn Oliver's secret identity in the not-too-distant future, possibly as early as tonight. I don't suspect it will be Malcolm as there is still some tension and suspense to build up on that front. To quote Guggenheim, the reveal will occur "in short order."
Colton Haynes will be joining the cast as Roy Harper, a love interest for Oliver's younger and wilder sister, Thea. Oliver is very protective of his sister and will have his doubts about his new guy in their lives, especially since he hails from a seedier side of town.
In a couple episodes we will get to meet The Count who will be played by Seth Gabel of Fringe fame. He is based on the Count Vertigo character from the Green Arrow comic and arrives on the scene as the producer of a drug known as "Vertigo," which also happens to be the name of the episode. Chalk up another bad guy for Arrow to set his sights on. Check him out getting surprised by Arrow above (via TV Guide).
Tonight's episode of Arrow that ends the short winter hiatus is titled 'Burned' and premieres at 8/7c on The CW. You can watch the episode online here, though not immediately live, shortly after it airs.