Three-episode crossover event featuring DC superheroes from 'Arrow', 'The Flash', 'Supergirl' and 'DC's Legends of Tomorrow'. When Barry Allen aka The Flash (Grant Gustin) investigates a meteor that's crashed outside Central City he discovers a race of aliens called the Dominators whose spaceship has crash-landed on Earth. To combat the threat of the alien race, Barry and his team at S.T.A.R. Labs join forces with Team Arrow, Supergirl (Melissa Benoist) and the Legends of Tomorrow to save the planet from the extraterrestrial threat.