The Flash returned Tuesday night, picking up one of the pre-"Crisis on Infinite Earth" threads with Iris' investigation into the mysterious organization behind various terroristic crimes as well as the weaponization of various metahumans. While Iris pursued that story, however, some of the major changes to reality that came with the creation of Earth-Prime began to take shape and for one member of Team Flash, those changes resulted in a change in purpose and may just have led to a major goodbye.
Spoilers for The Flash midseason premiere, "Marathon", below.
One of the major elements of "Marathon" beyond Iris' (Candice Patton) investigation of the mysterious and dangerous organization Black Hole was Cisco's (Carlos Valdes) struggle to make sense of and make peace with the new reality of Earth-Prime. Not only do we see Cisco struggle with the streamlined timeline and the idea that there are countless people who simply no longer exist - presumably including Team Flash's close Earth-2 friends Harry Wells and his daughter Jesse - but he is also struggling with the fact that the rebirth of reality has led to a major shakeup in the villain landscape. Old, familiar villains have wild new powers, some villains are entirely new imports from other worlds, others are new versions of old villains. For Cisco, it means that not only is Earth-Prime in serious danger, but it also is a situation in which Team Flash has some serious disadvantages. It also turns out that physics on Earth-Prime is a bit different than it was on Earth-1, which presumably means that some of Team Flash's tricks and weapons just won't work.
The entire situation is one that is exacerbated by Cisco's survivor's guilt and it ultimately leads him to leaving Team Flash with a very specific purpose. He's going to go out and compile all the differences between the way things are on Earth-Prime and the way they used to be on Earth-1, something that will provide a catalog of information for the heroes that can potentially help them deal with the new threats this reality faces. At the end of the episode, we see Cisco pack up and depart STAR Labs, leaving Nash (Tom Cavanagh) in charge in his absence.
It's not clear if this is an actual exit for Cisco (and Valdes), but if it does end up being a departure it won't come as a complete surprise. It has been rumored for some time that Valdes would be leaving The Flash with Cisco written out in such a way that the door would remain open for his return. It's worth noting, however, that the series did set up a fairly "perfect" avenue for exit for Cisco in the Season 5 finale, "Legacy", by having him take the metahuman cure so that he can have a normal life with his new girlfriend, Kamilla (Victoria Park). However, both Cisco and Kamilla have been fixtures in Season 6 and tonight's episode sets up Kamilla to have a continued role with Iris' Team Citizen as she works as the photographer for the Central City Citizen in addition to helping Team Flash.
Whatever ends up being the case, it's pretty clear that Cisco is no longer going to be part of the day-to-day operation of Team Flash and it will be interesting to see what that means for the heroes going forward.
The Flash airs Tuesdays at 8/7c on The CW.