‘A Monster Calls’ looks like it might be a great, touching film, but the upcoming family movie has a true and tragic story behind it.

Before A Monster Calls became a book by Patrick Ness, it was set to be the fifth novel by an author named Siobhan Dowd. Sadly, she passed away from cancer before she could do more than create a story outline. When he found it, Ness picked up the project and turned it into the book that the film is now based off of.

If you aren’t familiar with the story, it tells the tale of a 12-year-old-boy who is having trouble dealing with his mom’s illness. As a means of escape from his mother (Felicity Jones’) cancer treatments, he finds himself being visited by a giant tree (Liam Neeson) who takes him to a nearby graveyard and tells him stories.

A Monster Calls opens on December 23rd.