Tonight "Arrow" delivered an outstanding winter finale. The episode -- which was titled "What We Leave Behind" -- superbly showcased Prometheus' plan to bring down Team Arrow, while also providing an intense emotional landscape that allowed Oliver to address and grieve over the sins of his past. While never fully unmasking Prometheus (as was expected,) the episode did provide some clues as to his identity: the son of Justin Claybourne -- someone that Oliver killed off the list back in Season 1. While Oliver was dealing with the heavy emotional burdens in this episode, his team also suffered greatly at the hands of Prometheus. Curtis was attacked and may have ruined his marriage, Wild Dog and Rory were betrayed by Evelyn, Diggle was arrested, and Felicity's boyfriend Billy was killed. The episode concluded with the surprise return of Laurel Lance, which will have to be explained when the series returns in January. This episode may have been "Arrow's" strongest of the season, as it created space for Stephen Amell to deliver one of his finest performances on the show ever.

Prometheus' Hit List

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The episode kicked off in Prometheus' lair, where he outlined his plans to his inside woman, Artemis. On his wall he had the photos of everyone connected to Oliver Queen and the Green Arrow -- Felicity, Diggle, Lance, Thea, Curtis, Rene, and Rory. While Evelyn assumed that Prometheus wanted to kill Oliver, he said that he actually didn't want to kill him, he wanted to tear down his life and everyone in it. Prometheus began his attack by hurting Curtis, who collapsed on the steps of the Mayor's office after a town Christmas party. Curtis was rushed to the hospital, where he had to tell his husband the truth about being a member of Team Arrow. Later, when the team tracked Prometheus down to a warehouse, Evelyn revealed herself to the team as a traitor, because she believed that Star City needed to be saved from the Green Arrow. Artemis and Prometheus fled, but not before Oliver and the team discovered some key clues about Prometheus' identity.

Justin Claybourne

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While the team was investigating the warehouse and the chemical that Curtis was injected with, the team discovered a connection to a name Oliver had once crossed off his father's list. Here, the flashbacks took us not to Russia or a time Oliver was on the island, but to the Arrow Cave in Season 1. Oliver and Diggle were investigating an outbreak of tuberculosis and a pharmaceutical company that was profiting from the outbreak. Their search led them to Justin Claybourne -- the man responsible for weaponizing the outbreak and a name on the list. The flashbacks showed Oliver threatening Claybourne's life and when he didn't stop profiting from the outbreak Oliver shot and killed him. All of these scenes played out over a current timeline/flashback overlay, where Oliver retraced his steps at the chemical plant in both past and present. At first, Team Arrow thought that Prometheus was Justin Claybourne back from the dead, but when they found Justin's remains and a baby picture of his son, they knew Prometheus must be this unnamed child. Oliver came face to face with Prometheus in the same place that Justin Claybourne was killed, but instead of killing Prometheus, he killed Felicity's boyfriend Billy Malone. Billy was trapped inside the Prometheus suit and Oliver killed him by accident. When Oliver pulled Prometheus' mask off he was devastated to realize that he had killed an innocent man.

Oliver's Guilt

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Oliver then had to deliver the tragic news to his team and to Felicity. Stephen Amell's performance in this scene absolutely made the episode. In that moment Oliver was ashamed at what he had done, he was broken, he wanted to push everyone away from him because he was afraid they would all die at his hands. Felicity took the news the hardest, but instead of fleeing from Oliver, the team rallied around him. This guilt play was all part of Prometheus' plan to isolate Oliver, to get him to hit rock bottom -- as if other seasons of the show haven't already shown Oliver at his lowest point. Interestingly, this episode allowed for multiple motivational speeches, from Thea to Oliver's new girlfriend, Oliver was encouraged multiple times that all of the good he did for the city completely outweighed the bad and that he needed to learn to focus on the good. Ultimately Oliver was left to deal with the truth that doing something good -- crossing someone off his dad's list -- could also do something bad -- like create a mortal enemy.

The Canary Rises 

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The episode concluded with Curtis' husband leaving him, Evelyn off the team, Felicity in shock, the arrest of John Diggle, and the shocking return of Laurel Lance. When the show returns on Wednesday, January 25, 2017, it will have a lot to answer for, including the true identity of Prometheus. So far he's believed to be Claybourne's son, but that might be a misdirect. Some theories have been floating around that Prometheus could be Grant Wilson, Slade Wilson's son, which was hinted at when Prometheus threw a throwing star at Oliver's picture and it landed in his eye. Oliver did point out this week that whoever Prometheus is, he was trained by the same woman in Russia who trained Oliver -- is that a clue? As for Laurel, while it was previously announced that she would be returning to the show, she was not expected to return until the second half of the season. Laurel's arrival and the true identity of Prometheus may have something common, just like Felicity said this week, "Dead people show up alive pretty much every Wednesday."

Starring Stephen Amell as the Emerald Archer, "Arrow" airs Wednesdays at 8 pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey, John Barrowman, Willa Holland and more.