Sibéal Pounder is the author of the bestselling Witch Wars and Bad Mermaids series of books. Her debut, Witch Wars, was shortlisted for the Sainsbury's Children's Book Award and the Waterstones Children's Book Prize. Bad Mermaids Meet the Witches was a 2019 World Book Day title and a Sunday Times bestseller and has been optioned by Sony Animation. She has also written Beyond Platform 13, a sequel to Eva Ibbotson's The Secret of Platform 13, and her latest book Tinsel is all about a young girl called Blanche Claus and asks the question: what if a long time ago we all got the Santa story a bit wrong? Previously Sibéal worked as a journalist, writing for publications including the Guardian and Vogue Online and was a philanthropy columnist for the Financial Times.

Jason Cockcroft graduated from Falmouth School of Art in 1994 and has been working as an illustrator of children's books ever since. He won the Blue Peter Book Award for his work on Geraldine McCaughrean's retelling of A Pilgrim's Progress and was the illustrator on the original covers of the final three Harry Potter novels.

The film rights to the Bad Mermaids series have been optioned by Sony Pictures Animation