Following the events of 'Battle for Mewni', Star and Marco begin to carry on with their lives while trying to work through wrinkles in their friendship as it is tested in new ways. Meanwhile, an unfrozen Eclipsa Butterfly seeks contentment in a new, unforgiving age. Centuries-old secrets which left scars on the Butterfly family's history are starting to unravel, even when the only person left who remembered it all disappeared along with it. As the the long-hidden truth is finally uncovered, sooner or later someone will have to pay.