Tonight's episode of Arrow saw a long-time character leave the show, but it also may have just brought back a major element of the series... sort of.
Spoilers for tonight's episode of Arrow, "The Thanatos Guild", below.
Tonight's episode saw Nyssa al Ghul (Katrina Law) return to Star City as a rogue offshoot of the League formed by the late Malcom Merlyn -- the Thanatos Guild -- was hunting Thea (Willa Holland). Turns out the Guild needed Thea to open a mysterious box containing a map, but why that map was so important was a surprise that Thea and Team Arrow didn't quite see coming.
After getting the cube away from the Guild, Thea -- with help from Felicity's (Emily Bett Rickards) knowledge of mathematics -- was able to open it and retrieve the mysterious map. However, the map appeared to be blank, and none of the tricks the team was used to using to read secret League text worked. The Guild also hadn't stopped hunting Thea, either, determined to spill her blood. It turns out the blood thing is literal.
You see, the map really could only be accessed by Thea. Her blood was what was needed to cause the details of the map to appear, and when it does, everyone is shocked to discover that the lay lines on the map appear to lead to three locations -- three previously unknown Lazarus Pits.
This is definitely not a good thing. On Arrow -- and to an extent in DC Comics lore in general -- the Lazarus Pit was a pool of waters that allowed the person immersed in it to heal themselves of wounds, prevent aging, and even come back from the dead. On Arrow, Ra's al Ghul owned the only known pool until his death. Nyssa destroyed the pit when Malcom (John Barrowman) used it to resurrect Sara Lance (Caity Lotz) without her soul. The pit was also used on Thea Queen, who experienced a disturbing bloodlust after having been brought back from the dead.
The discovery of three new Lazarus Pits isn't something Thea expected to hear, but it's also not entirely surprising. With Malcom having presumably been killed on Lian Yu during the Season Five season finale, the existence of these Pits could provide the Guild a means to bring him back to life so that he can lead them once again. This is something that Nyssa cannot allow, and Thea isn't inclined to allow Malcom a chance to return and resume his villainous pursuits, either. She ultimately decides to go with Nyssa to locate and destroy those Lazarus Pits -- and Roy Harper (Colton Haynes) chooses to go with her as well.
Arrow airs Thursdays at 9/8c on The CW.