[This is a review of Legends of Tomorrow season 2, episode 7. There will be SPOILERS.]

Throughout its second season of time-travel adventures, Legends of Tomorrow has weaved its visits to various historical time periods in with a number of mysteries -- including the disappearance of Rip Hunter, the murder of Rex Tyler, and the endgame of the burgeoning Legion of Doom. Furthermore, thanks to the loss of Rip and the addition of new crew members aboard the Waverider in Nate Heywood and Amaya Jiwe, Legends of Tomorrow experienced a cast shakeup that provided for a fresh perspective in season 2.

However, although last week's sojourn to the Old West offered little to the overarching storyline -- despite being an entertaining detour that featured Jonah Hex (Johnathon Schaech) -- 'Outlaw Country' did see the team gather enough dwarf star alloy that Ray Palmer could create a new Atom suit. That suit has come in handy this week as Ray and his fellow Legends returned to Earth to help their friends from Supergirl, The Flash, and Arrow battle against the Dominators in a massive three-hour event.

The crossover concludes in this week's Legends of Tomorrow episode, 'Invasion!' -- with a story by  Greg Berlanti, teleplay by Phil Klemmer and Marc Guggenheim, and directed by Gregory Smith. In the episode, the team of superheroes learn of the Dominators' plan for their Earth and they must figure out a way to defeat the alien race once and for all. However, Professor Stein is distracted by an aberration he created while the Legends were in 1987.

A Star Spangled Idiot in 1951

Steel and Supergirl in Invasion!

Legends of Tomorrow's 'Invasion!' features plenty of characters from its fellow DC TV series -- though Supergirl is relegated to an exceptionally small role with the thin explanation that having an alien on the team is too weird for Oliver Queen. Still, the members of the Legends team run point on the various missions in the early part of the episode. Nate, Amaya and Mick take Cisco and Felicity along to 1951 in order to capture a Dominator and question it about the aliens' intentions.

The storyline features Nate's Citizen Steel suit in action -- with Mick offering the surly quip that he looks like a "star-spangled idiot" -- as he, Vixen and Heat Wave take down a Dominator. Though they're waylaid by a younger version of Agent Smith (introduced in The Flash's 'Invasion!' episode), they're saved by tech support, otherwise known as Cisco and Felicity. Before escaping, the group decides to help free the Dominator as well, saving him from torture at the hands of the U.S. government.

However, the adventure to 1951 is relatively short-lived, which epitomizes how Legends of Tomorrow compromised much of the show's ongoing storylines for the sake of the mega-crossover. Certainly, each series within the crossover was forced to abandon their larger season arcs in order to come together and focus on the heroes fighting aliens. And, with the influx of characters, 'Invasion!' also attempted to juggle a number of character arcs, some of which were more successful than others.

With so much going on in 'Invasion!', it's no wonder the trip to 1951 was relatively brief, and it's certainly commendable that the Arrowverse writers were able to include a time travel element within the larger crossover story arc in order to stick to the Legends of Tomorrow premise. Plus, with the addition of Cisco and Felicity, who are both newcomers to the Waverider and experience time travel for the first time, this aspect of 'Invasion!' is one of the more entertaining storylines.

It All Comes Back to Flashpoint

Legends of Tomorrow Invasion! Promo

In the season 3 premiere of The Flash, Barry had been living in an alternate timeline he created by saving his mother -- what has been dubbed Flashpoint. But, when he tried to set the timeline back to the way it had been, Barry ended up changing certain aspects of his and his friends' lives. Although Oliver warned Barry in The Flash's 'Invasion!' that the assembled superheroes could only deal with one sci-fi problem at a time, Legends of Tomorrow's 'Invasion!' revealed the problems were one in the same -- the Dominators had come to Earth in 2016 as a result of Flashpoint.

Overall, the reasoning for the Dominators' arrival on Earth and the winding path the heroes are forced to travel to figure it out is convoluted and, eventually, only explained through a few lines of dialogue. Additionally, as is pointed out by Cisco within 'Invasion!', the Dominators' reasoning doesn't make much sense: The Dominators are afraid that metahumans will destroy Earth and extend that destruction to other worlds, despite the cruelty they're shown by humans and the heroism of metas like Cisco and Barry. It's a wave of the hand explanation in order to position the Dominators as villains without offering the aliens much character depth.

Of course, an underdeveloped villain isn't necessarily a new issue within live-action superhero media, especially in the Arrowverse -- though it is no less frustrating. Still, while 'Invasion!' may not have provided a compelling villain, the crossover does conclude in a somewhat exciting battle sequence and a fanservice-filled after party for the heroes once they've won the day. Between the battle featuring the main heroes from all of The CW's DC TV series and a party sequence showcasing various fun character interactions and on the nose in jokes, 'Invasion!' provides something for every fan.

Stein’s Aberration & Cisco's Time Travel Lesson

Legends of Tomorrow Invasion Stein and Jax talk while sitting

Acting as the grounded character arcs of 'Invasion!' are Stein's relationship with his newfound daughter Lily (Christina Brucato) and Cisco's continued bitterness toward Barry for Flashpoint. Stein's distance from Lily and his revelation to Caitlin that he believes his daughter to simply be a an aberration are well-acted by Garber, who carries the arc well. However, with so much else going on and Stein's daughter only tangentially related to the mission at hand, this particular storyline falls victim to an overstuffed episode. But, with Jax now in on Stein's secret, it's clear Lily's existence will be revisited in later episodes.

Meanwhile, Cisco learns through his trip to 1951 that anyone can create problems in the present or future by changing the timeline trying to do the right thing. The revelation gives him much needed perspective on Flashpoint and his own bitterness toward Barry for altering the timeline in a way that meant Cisco lost his brother. Certainly, Cisco's arc struggles within the confines of the crossover episode but, more so than Stein, his storyline fits well into the overarching narrative.

Of course, with the Dominators defeated at the end of 'Invasion!', and the heroes from Supergirl, The Flash, and Arrow returning to their home cities while the Legends depart in the Waverider, Legends of Tomorrow will return to its regular season 2 storyline. With the midseason break looming, it remains to be seen how Legends of Tomorrow develops and capitalizes on its ongoing narratives -- like the Legion of Doom.

Legends of Tomorrow continues Thursday, December 8 with 'The Chicago Way' at 8pm on The CW.