Watch The Flash Season 9 Online Free. After defeating the Reverse Flash once and for all, Barry Allen and Iris West-Allen are reconnecting and growing closer than ever before. But when a deadly group of Rogues descend on Central City led by a powerful new threat, The Flash and his team must once again defy impossible odds to save the day. But as The Rogues are defeated, a deadly new adversary rises to challenge Barry Allen’s heroic legacy. And in their greatest battle yet, Barry and Team Flash will be pushed to their limits, in order to save Central City one last time.