Based on the book series of the same name by Jill Murphy, the series follows Mildred Hubble (Bella Ramsey and Lydia Page) and her friends Maud Spellbody (Meibh Campbell and Megan Hughes) and Enid Nightshade (Tamara Smart), and rivals Ethel Hallow (Jenny Richardson), Drusilla Paddock (Tallulah Milligan) on their adventures and education at Cackle's Academy under caring headmistress Miss Cackle (Clare Higgins) and strict deputy headmistress Miss Hardbroom (Raquel Cassidy).

With the help of her new friend Maud Spellbody, Mildred goes to an academy for witches and is admitted after she saves it from the headmistress Miss Cackle's evil sister Agatha whose magic is later taken away.

While Mildred, Maud, Enid, and the Hallow sisters search for a way to re-ignite the founding stone, Mildred stumbles upon her ancestor on her family tree and learns the Hubbles are a witching family but Mirabelle, her ancestor, sacrificed her and twelve generations of magic to re-ignite the founding stone.

Mildred starts the spell but half-way through, Miss Mould, the art teacher, takes her place and sacrifices her magic.

Miss Cackle invites Mildred's mum Julie to teach art at Cackle's; however, Julie is treated horribly by Miss Hardbroom, the potions teacher, causing Mildred to steal a wishing star and make her mum magical.

Mildred withdraws from the competition but finds water that can tell the future and sees Ethel as head girl in front of empty chairs.

Ethel frees Agatha from a photograph Miss Cackle trapped her in and Maud learns Mildred was framed.

Spell science teacher Mr Daisy makes a potion which turns Miss Cackle back to herself who says the name, taking everyone out of vanishment.

[19] Tamara Smart gained the part of Enid Nightshade after four months of auditioning, which she described as "very long" yet "nerve racking but at the same time very exciting".

[20] Jenny Richardson and Miriam Petche were cast as sisters Ethel and Esmerelda Hallow.

[21][22] Tallulah Milligan, the daughter of Coronation Street and Waterloo Road actress Angela Griffin, was cast as Drusilla Paddock.

[25] Bella Ramsey described filming as being "really good" but said there were some challenging elements and described learning the stunts as "hard".

[27] Common Sense Media favourably compared it to Harry Potter though it was "quirkier" and "less scary".