Tonight on Arrow, Oliver Queen headed to Hong Kong to find a scientist necessary to help The Monitor save the multiverse from destruction in the upcoming "Crisis on Infinite Earths" storyline. As with last week, when the hero had to head to Earth-2 to obtain some dwarf star allow, The Monitor declined to give Oliver any specifics as to the "why" of his mission, saying only that it was Oliver's job to obey him and deliver what he needed. After an esoteric material from Earth-2 and a brilliant scientist on Earth-1, though, it seems possible (if not likely) that fans of the comics can guess what it is that The Monitor and Green Arrow are doing together.
It seems likely the pair are assembling the necessary elements to construct a Cosmic Tuning Fork. Key to the events of Crisis on Infinite Earths, Infinite Crisis, and Dark Nights: Metal in the comics, the Cosmic Tuning Forks (or tuning towers) were giant structures built by the Monitor during Crisis on Infinite Earths, which helped to slow the merging of multiple earths during the Crisis.
Basically, since the universes in DC's multiverse occupy the same physical space but are separated by different "vibrational frequencies." One of the ways The Anti-Monitor hoped to destroy all of reality was to cause the remaining Earths he had not already destroyed to vibrate at the same rate, ultimately colliding into one another and causing a cataclysmic event. The tuning forks helped to slow that event by stabilizing and even controlling rates of cosmic vibration. It seems likely that, at some point in the "Crisis" crossover happening this winter, such a tool will come into play for the Arrowverse as well.
"Crisis on Infinite Earths" has loomed over the Arrowverse for years. The series premiere of The Flash featured an allusion to the hero disappearing amid red skies in the year 2024. During the original comics event, red skies were a sign of doom to come to a world during the Crisis. At the end of last season, a couple of things happened: The Monitor (LaMonica Garrett), who had appeared in "Elseworlds," reappeared and revealed that Oliver Queen was destined to die in the Crisis...and the future newspaper at STAR Labs rolled back the expected date of the Crisis from 2024 to 2019.
In the comics, Crisis on Infinite Earths centered on a battle between the combined superheroes (and even some villains) of the DC multiverse and an immortal, cosmic threat known as the Anti-Monitor. Like The Monitor, the Anti-Monitor will be played by LaMonica Garrett in the Arrowverse. As the Anti-Monitor destroys realities, he replaces their positive matter energy with antimatter, growing his own power and sphere of influence. He was eventually stopped by the sacrifices of several heroes, including The Flash and Supergirl, as well as the merging of multiple universes to save reality by becoming a single, unified timeline. Fans have long wondered whether the events of "Crisis on Infinite Earths" might bring Supergirl and even Black Lightning to Earth-1, where the rest of the series take place. The crossover will also feature guest appearances by Tom Welling as Clark Kent, Erica Durance as Lois Lane, John Wesley Shipp as the Flash of Earth-90, Johnathon Schaech as Jonah Hex, Kevin Conroy as Bruce Wayne, and Ashley Scott as The Huntress.
“Crisis on Infinite Earths” kicks off on Sunday, December 8 on Supergirl, runs through a Monday episode of Batwoman and that Tuesday’s episode of The Flash. That will be the midseason cliffhanger, as the shows go on hiatus for the holidays and return on January 14 to finish out the event with the midseason premiere of Arrow and a "special episode" of DC's Legends of Tomorrow, which launches as a midseason series this year and so will not have an episode on the air before the Crisis.