In tonight's episode of "The Flash," Barry Allen will discover the "Arrow"-verse's biggest threat to date: the Dominators. When push comes to shove, he organizes all the heroes he knows -- from Team Arrow to the Legends of Tomorrow to Supergirl -- in order to put a stop to this alien invasion. However, a group that large needs a leader, and Barry may have just found himself in the captain's chair.
Of course, that doesn't mean Oliver isn't calling some of the shots. When Barry struggles to come up with their next step, Green Arrow suggests using Supergirl as practice; since Kara is strong and nigh invincible, she'll make an excellent test for the equally strong, mind-controlling Dominators.
Barry calls Kara and Oliver aside for a more personal introduction that leaves Kara a little puzzled and wondering if Oliver doesn't quite like her, only for Barry to assure her that he treats everyone that way. However, Oliver made one thing abundantly clear: she shouldn't hold back on them, and especially not on him.
The clip also proves that there's still plenty of tension between Barry and Cisco, who found out that his brother Dante had not died before Barry created the Flashpoint timeline. When the Atom suggests a vote for team leader, Cisco immediately throws in for Oliver, much to Barry's disappointment.
Once in the “Arrow”-verse, Supergirl will join the Flash, Green Arrow, the Legends of Tomorrow and their friends in order to stop an alien invasion. With them, she’ll face down the Dominators, mind-controlling aliens who have grown so concerned about Earth’s metahuman threat that they have decided to stomp it out before it can reach the stars.
Starring Melissa Benoist as the Girl of Steel, “Supergirl” airs Mondays at 8 pm ET/PT on The CW. The network is also home to Grant Gustin as the Scarlet Speedster in “The Flash,” airing Tuesdays at 8 pm ET/PT, Stephen Amell as the Emerald Archer in “Arrow,” airing Wednesdays at 8 pm ET/PT and Arthur Darvill, Brandon Routh and Caity Lotz in “DC’s Legends of Tomorrow,” airing Thursdays at 8 pm ET/PT.