Based on "The Little Broomstick" by Mary Stewart, a strange flower grants a girl magic powers.

Mary is an ordinary young girl stuck in the country with her Great-Aunt Charlotte and seemingly no adventures or friends in sight. She follows a mysterious cat into the nearby forest, where she discovers an old broomstick and the strange Fly-by-Night flower, a rare plant that blossoms only once every seven years and only in that forest. Together the flower and the broomstick whisk Mary above the clouds and far away to Endor College - a school of magic run by headmistress Madam Mumblechook and the brilliant Doctor Dee. But there are terrible things happening at the school, and, when Mary tells a lie, she must risk her life to try to set things right. Based on Mary Stewart's 1971 classic children's book "The Little Broomstick", "Mary and The Witch's Flower" is an action-packed film full of jaw-dropping imaginative worlds, ingenious characters, and the stirring, heartfelt story of a young girl trying to find a place in the world. Featuring the voices of Ruby Barnhill and Academy Award-winners Kate Winslet and Jim Broadbent.

A magical laboratory has caught fire. A red-haired girl slips away with a satchel, but is seen and pursued. The girl manages to escape on her flying broomstick, but a massive explosion knocks her off her broomstick. The broomstick and satchel fall to the ground. Out of the satchel spill magic seeds, which cause the plants and animals in the area to rapidly grow. Young Mary Smith moves into the British estate of her Great Aunt Charlotte. The bored, friendless girl creates messes as she tries to make herself useful through chores. A local boy named Peter teases her for both her clumsiness and her wild red hair, which she hates..