|"Things were looking a little grim, but part of me was, admittedly, a little excited for a "reunion" of old friends."|
- "Run, Barry. Run."
- —Oliver Queen encouraging Barry Allen to save himself and escape from Vandal Savage.
|Oliver and Barry Allen take Kendra Saunders and Carter Hall to a remote location to keep them hidden from Vandal Savage while they figure out how to defeat him. Malcolm arranges a meeting between Vandal, Green Arrow and The Flash that doesn't go as planned. Meanwhile, Felicity, Thea, Diggle and Laurel work with Team Flash to come up with a weapon powerful enough to destroy Vandal Savage.|
In a flashback from Egyptian Middle Kingdom, It is revealed that in their past lives, Kendra was known as Chay-Ara, Priestess of Horus, and Carter was Khufu, the Prince of Egypt and Vandal Savage was known as Hath-Set, a priest and advisor to Ramesses II. Chay-Ara and Khufu were romantically involved.
In the present day, Team Arrow arrives at Central CIty and take lodgings in a house in the city's suburbs. Oliver goes alone to see Samantha Clayton, as he suspects he is the father of her son, William. To confirm it, he manages to take a hair sample from the boy's cap. Malcolm Merlyn has arranged a meeting with Vandal Savage, in which Oliver, Barry and he takes part. While running to the meeting place, Barry notices himself running alongside himself the same way he did before. In the meeting, Vandal demands the heroes give up Chay-Ara and Khufu in 24 hours or else he destroys Central City.
Oliver and Barry deliver Vandal's ultimatum and the group goes on to do separate things: Cisco goes to work on protective gloves against Vandal's Staff of Horus, where Barry informs him about seeing himself, distressing Cisco; Carter takes Kendra to train in order for her to awaken, telling her to strike at him, briefly awakening through anger.
Oliver has Barry run a test on the hair sample he obtained, which confirms his suspicions. He tells Barry not to tell anyone about this, but just as he leaves Felicity shows up, and Barry's attempt to hide the test result fails, and Felicity discovers that Oliver had Barry run a paternity test.
Oliver returns to Samantha and tells her he knows. Samantha reveals that Moira Queen paid her million dollars to tell Oliver she lost the child and shows the check as proof. She then came to Central City to stay far away from her. Oliver wants an opportunity to get to know William, but Samantha demands that he won't tell anyone, to which Oliver doesn't agree.
Oliver returns to the house and meets angry Felicity. As Oliver tries to evade the subject, Felicity claims she doesn't care Oliver has an illegitimate child, but she cares how he lied to her again, breaking up with him. Barry then takes Oliver that it's time to go to meet Savage. Oliver's plan involves only him, Barry, Kendra and Carter, thinking that Vandal's ignorance about Kendra's awakening works to their advantage. The plan goes awry when it is learned that Cisco's gloves aren't working against the Staff and Kendra is unable to awaken. Vandal kills Kendra and Carter and the uses the Staff to cause a massive blast that obliterates the city, Oliver and everyone else. Barry is able to escape due to his super speed, and then finds himself travelling back to the past, to the time he, Oliver and Malcolm met with Savage.
Now aware what will transpire, Barry tells Oliver that he is a father to someone and that it will end badly with Felicity, and that he is also not in the right mind to face Savage. Oliver takes Barry's word and says they are going to do things differently this time.
Oliver goes to Cisco and asks him to talk with Kendra, since Carter's methods aren't working. Cisco does so and he suggests that Kendra focus on the priestess rather than warrior in her. Cisco manages to get Kendra to allow herself remember what happened when Savage killed her and Carter the first time.
Kendra has a flashback from 4000 years ago, when Savage caught her as Chay-Ara and Carter as Khufu in bed together and declares that sleeping with the holy priestess is a punishable with death. As Khufu and Savage fight, a large meteorite strikes the palace and Savage kills Khufu and Chay-Ara. Savage then declared that his anger is everlasting, that the cycle will never end, thus becoming Immortal. Chay-Ara, in her death throes, prays to Horus, and she and Khufu receive Horus' blessing, and starting the cycle of their deaths and rebirths. Chay-Ara also witness that shards of the meteorite was glowing with blue hue. Awaking in the present, Kendra thinks she discovered the way to defeat Savage.
Kendra has everyone assembled and reveals to what she saw, surprising Carter as he has never been able to remember their first death. Kendra believes that the material from the meteorite that crashed that day may be the key and Felicity confirms that Egypt was hit with a lot of meteors during the Middle Kingdom. Cisco realizes that the gloves won't work because they are missing a key component, like an Nth Metal. Barry runs to obtain a meteorite shard and Cisco adds it to the gloves. Oliver then tells it's time to go and, unlike last time, he tells Diggle, Thea and Laurel to suit up.
At the meeting, things go differently this time as Team Arrow is able to distract Savage and Kendra is now able to fight. Barry manages to grab the Staff and this time the gloves work. Eventually Savage is defeated and he turns to dust.
Oliver, Barry, Cisco, Kendra and Carter think about the future, as this is new to Kendra and Carter, since they have never been able to defeat Savage before. Kendra agrees to go with Carter and says her farewell to Cisco. Oliver and Barry discuss William and Barry suggests that he should be there for him. Oliver goes to Samantha and this time Oliver agrees to her condition that he won't tell anyone about him, not even Felicity. He then has a moment with his son as they play with action figures.
Oliver and Felicity return to Star City and share a moment together. In Central City, Malcolm goes to Savage's remains and collects them while reiterating the Savage's chant.
Preparation ran from September 22 until September 30, 2015. Shooting ran from October 1 until October 15, 2015.
- This episode marks the shortest appearance of Star City on , as the city only appeared during the final scene. Most of the episode takes place in Central City.
- This is one of the only episodes of before Season 6 that doesn't feature the flashback storyline at all.
- Despite this being an episode, lightning transition graphic is still used during the episode.
- The title of this episode likely refers to the fact that Barry traveled back in time to the previous day after Vandal Savage destroyed Central City by unleashing a devastating energy blast from the Staff of Horus.
- Barry running from Vandal Savage's blast that destroys Central City is a reference to a scene from Justice League: The Flashpoint Paradox where Barry runs from a similar blast in the movie created by Aquaman's Captain Atom-powered bomb.
- This episode is included in Season 2 home release.
- Thea mentions seeing a movie with "a bunch of superheroes in a farmhouse", probably referencing Avengers: Age of Ultron, where the heroes hid in Hawkeye's farmhouse.
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