Star is Mildred's Dog, who she finds in her fourth year at Cackle's

In her fourth year, Mildred is made Lantern Monitor. She sees a shooting star and makes a wish, which comes true when she finds a stray dog while on her lantern round; it is revealed to the reader that the dog's previous owner mistreated him before leaving him in the forest. Mildred names the dog Star, and trains him to ride on her broomstick while taking him for walks in the mornings and evenings in her role as Lantern Monitor. At the same time, Cackle’s Academy enters a competition which to win a swimming pool; they compete against Pentangle's Academy and Moonridge High School. Each school must put on an act, and three judges will choose the winner; Cackle’s act is a broomstick ballet.

On the morning of the competition, Mildred has an altercation with Ethel when Ethel spots Star moving in Mildred's bag, which results in the ballet costumes being destroyed, but Maud and Enid have an idea: They suggest that Mildred and Star could perform their broomstick tricks, as a replacement for the ballet. The judges consider the act unusal, but declare Mildred and Star as the winners! Miss Cackle says she was impressed by Mildred's performance, and allows her to keep Star, and to use him as her Broomstick Companion, while Tabby is retained as a more standard companion.