The latest episode of The Flash offers a shred of hope for Barry Allen (Grant Gustin) in the form of Nash Wells (Tom Cavanagh). So far, The Flash's sixth season has dealt primarily with Barry's impending demise. Ever since the pilot episode, it was teased that Barry would vanish in a mysterious Crisis, and it was recently confirmed that Barry's fate had been moved up to 2019, which means that this storyline will play out in the upcoming Arrowverse crossover, "Crisis on Infinite Earths". Over the last few episodes, Barry, his friends, and his family have all struggled to accept the Monitor's promise that Barry must die for the Earth to survive the Crisis.
Earlier this season, The Flash brought in a new version of Tom Cavanagh's Harrison Wells, Nash Wells, and this character apparently has a mysterious connection to the being who foretold Barry's death, the Monitor (LaMonica Garrett). In his first appearance, Nash was introduced as a multiverse explorer styled after Indiana Jones on the hunt for Eternium. Later, he helped Barry and Cisco (Carlos Valdez) recover a serum in exchange for a device called a crypto-circuit. Using the crypto-circuit, he tracked down a holographic projection of the Monitor, which suggested that Nash may factor into the story of "Crisis on Infinite Earths".
In The Flash season 6, episode 5, titled "Kiss Kiss Breach Breach", Nash and Joe (Jesse L. Martin) are trapped in the same tunnels where he followed the Monitor until they are saved by Ralph (Hartley Sawyer). Afterward, Nash overhears a conversation about the Monitor and Barry's fate. Nash then tells them to return to the tunnels later, because he knows how to save Barry. Whether he's telling the truth or not, it's certainly possible that Nash has knowledge about the Monitor that could be of value, and could even help Barry avoid his coming demise.
A cosmic entity has assured them that Barry can't be saved, so how can a human like Nash Wells solve this problem? It's been speculated that Nash is actually Tom Cavanagh's "Crisis" character, Pariah. If this is the case, the comic books could hold a clue. In the comic book version of "Crisis on Infinite Earths", Pariah was a scientist devoted to unlocking the secrets of the universe.
Nash and Pariah could be one and the same, since both are interested in hunting down the Monitor. If Nash, like his comic book counterpart, has an understanding of the universe that most mortals don't share, he could have access to information, or have come across something on his travels, that could be vital to making sure Barry sticks around after the Crisis is over.