Having thwarted Bowser's previous plot to marry Princess Peach, Mario and Luigi now face a fresh threat in Bowser Jr., who is determined to liberate his father from captivity and restore the family legacy. Alongside companions new and old, the brothers travel across the stars to stop the young heir's crusade.

Soon after the Thompson family’s arrival in the countryside, the three children – Joe, Beth, and Fran – discover a magical tree and its extraordinary and eccentric residents, including Moonface, Silky, Dame Washalot, and Saucepan Man. At the top of the tree, they're transported to spectacular and fantastical lands and, through the joys and challenges of their adventures, the Thompsons learn to reconnect and value each other for the first time in years.

Disowned at birth by his obscenely wealthy family, blue-collar Becket Redfellow will stop at nothing to reclaim his inheritance, no matter how many relatives stand in his way.