The CW's "Invasion!" crossover fully kicked off tonight on "The Flash." After traveling to Earth-38 to get the Girl of Steel herself, Barry knew he needed a whole team to take on the threat of the invading and hostile Dominators. From Team Arrow Barry recruited Oliver, Felicity, Diggle, and Thea. From Team Legends he recruited Sara, Mick, Jax, Stein, and Ray. Along with Cisco and Caitlin, this team of Super Friends began training with Supergirl to test their abilities in fighting aliens. Unfortunately, their training turned deadly when the Dominators kidnapped the President and lured most of the team into a trap. More Flashpoint secrets were revealed tonight, including Future Barry's message to the Legends, which warned of an impending war. Wally continued to test his Kid Flash powers this week, even at the dismay of his sister Iris, who was more concerned with keeping his safe than seeing him run at super-speed. The episode finished in the middle of a cliffhanger, with all of Team Arrow abducted by the Dominators. The crossover will continue on "Arrow" Wednesday evening and conclude on "Legends of Tomorrow" this Thursday.

Welcome to Earth-38

During "Supergirl's" first season, while she was still on CBS, Barry accidentally ran to her Earth. They became instant friends and Kara promised that if Barry ever needed her, she would come to his aid. Barry called in that favor tonight after discovering an alien spacecraft that landed in Cental City. As Lyla pointed out, the Dominators had been to Earth before, back in the 1950's. They were considered a hostile race who had used humans for experimentation. The Dominators had not been heard from since that time, until tonight. Lyla urged Barry to stay out of the fight but Barry wouldn't be Barry if he didn't hero up and try to save the day. Remembering Kara's favor, Barry and Cisco opened a portal to Earth-38 and Kara agreed to help. It was refreshing to see Kara on "The Flash" tonight, especially since she's usually a solo superhero on "Supergirl."

Super Friends Team-Up

Kara wasn't the only person whom Barry recruited -- he immediately went to Star City to recruit Team Arrow. While Thea has sat out most of "Arrow" this season as Speedy she jumped at the chance to take on aliens. Oliver and Diggle were also about to capture Vigilante when Barry raced them off, which hilariously left Diggle barfing over the balcony of Felicity's apartment. With Team Flash and Team Arrow assembled, Felicity sent coordinates through time and the Legends came blazing in on the Waverider. It was amazing to see all of the DCTV heroes assembled together -- Professor Stein got to be reunited with Caitlin, Felicity and Cisco got to tech-out together, and Barry and Kara were as charming as ever. The team decided to appoint a leader -- which almost fell to Oliver. Oliver nominated Barry, who had the team begin training with Supergirl. The S.T.A.R. Labs hanger where they were training was designed to look just like the Hall of Justice from Super Friends -- one of the many Super Friends Easter eggs in this crossover.

Flashpoint Continues to Damage the Timeline

While the Legends were in town, Jax and Professor Stein played Barry and Oliver Barry's message from the future. Barry's voice sounded wartorn and he warned the Legends about the damage he did to the timeline. Barry did not name Flashpoint in the recording, so he could be referring to a future event, but Jax, Stein, and Oliver all interpreted it to mean Flashpoint. Just before Barry sent the team to rescue the President Cisco found the tape and told Barry he had to tell everyone the truth. This part of the episode was incredibly emotional -- everyone was supposed to be focused -- but couldn't keep their composure when Barry began to tell them about what everyone had lost (or gained.) Cisco had lost Dante, Diggle lost Baby Sara, Caitlin had powers, Stein even had a daughter. Barry's choice to go back and save his parents held up a mirror to both Sara and Oliver. Sara claimed she refused to use time travel to save Laurel (although we've seen her try numerous times.) Oliver, on the other hand, was surprisingly supportive of Barry's choice to go back, admitting that if he had the chance, he would go back in time to save his mom and dad too. Oliver encouraged Barry to stop beating himself over what happened and reminded him again that he wasn't God. This keeps coming up for Barry, who is seeing what a Speedster God looks like, in Savitar.

Mind Control Strikes Again

Due to Barry's confession regarding Flashpoint, no one was willing to fight alongside him, expect Oliver. Barry and Oliver have known each other from the first crossover episode back in "Arrow" Season 2, even before Barry had powers, so it was touching to see Oliver defend Barry that way. Barry sent Supergirl to lead the team and rescue the President. Unfortunately, the President was bait in the Dominator's trap for the heroes. The President was killed once the team was inside the trap and the Dominators began to control them through telepathy. When the team returned to S.T.A.R. Labs it was Barry and Oliver versus everyone else. When Wally tried to get into the fight as Kid Flash he ended up hurt in the crossfire. Oliver had to carry him to safety while fending off Thea, Sara, Heat Wave, and Diggle. Barry lured Firestorm, the Atom, and Supergirl away, and then used Kara's strength to destroy the mind control device. Everyone landed back at S.T.A.R. Labs safely until Team Arrow was teleported off Earth and onto the Dominator's ship.

Kid Flash & The Flash Museum 

While most of the episode was focused on the crossover elements, two very significant elements came together that continued this season's storyline on "The Flash." First, H.R. pitched the idea of a S.T.A.R. Labs Museum. This seems to be the show's version of the famous Flash Museum from the comic books. If so, that will be amazing to see come together over the course of this season. Second, Wally decided to embrace his hero identity as Kid Flash. When Barry and Oliver were in trouble, he came to their rescue. He might be untrained, he might not be ready -- as Iris suggested -- but he is willing to put his own life at risk, which is the key component to becoming a hero. At the end of the episode, H.R. agreed to train Wally in secret. Wally's journey to fully becoming Kid Flash will continue to develop, especially in next week's Christmas episode.

The Crossover Continues 

Tomorrow night the crossover continues on “Arrow’s” 100th episode. Oliver, Diggle, Sara, Felicity, Ray, and Thea will all find themselves in a shared hallucination on the Dominator’s ship. As they struggle with determining what is real and what is fantasy, they will be met by many familiar friends and enemies, including Robert and Moira Queen, Deathstroke, and the recently departed Laurel Lance. The episode is set to celebrate all that "Arrow" has accomplished over 100 episodes, plus tie into the crossover.

When "The Flash" returns next week, Barry will travel to Earth-3 to seek the help of Jay Garrick. John Wesley Shipp and Mark Hamill both guest star in the episode -- titled "The Present" -- which will serve as "The Flash's" mid-season finale.

BARRY SEEKS HELP FROM JAY GARRICK — With Alchemy and Savitar still looming threats, Barry (Grant Gustin) is unable to focus on the Christmas holiday, and especially his relationship with Iris (Candice Patton). Determined to stop Savitar, Barry goes to Earth-3 to get advice from Jay Garrick (guest star John Wesley Shipp). Wally (Keiynan Lonsdale) wants to help Barry fight Savitar and reveals that he’s been training with H.R. (Tom Cavanagh), which doesn’t go over well with Barry. As Cisco (Carlos Valdes) faces his first Christmas without his brother Dante (guest star Nicholas Gonzalez), old wounds are reopened. Rachel Talalay directed the episode with story by Aaron Helbing & Todd Helbing and teleplay by Lauren Certo (#309). Original airdate 12/6/2016.

Starring Grant Gustin as the Scarlet Speedster, “The Flash” airs Tuesdays at 8 pm ET/PT on The CW. The series also stars Jesse L. Martin, Tom Cavanagh, Carlos Valdes, Candice Patton, Danielle Panabaker, Keiynan Lonsdale and more.