In the 1960s, a solicitor—Mr. Blunden—arranges for a widow and her children to move to an English house while the rightful heir is tracked down. The two children, Lucy and Jamie, soon meet two orphans, Sara and Georgie, who are living in the house—with their own version Mr. Blunden—exactly one century before! The orphans need help, so with the aid of a magic potion, Lucy and Jamie go back in time to the very day before the orphans will die in a fire (according to the gravestone that Lucy and Jamie found). They definitely have a fix-the-past mission, and they definitely succeed, but in the process, an amazing twist on the grandfather paradox arises (see the spoiler below).

The story has a kind of reverse grandfather paradox: [spoiler Lucy and Jamie’s great-great-grandparents are Sara and Tom (a boy who died trying to save Sara and George). So, initially, Lucy and Jamie actually have no grandparents (at least not on that side), and it’s only by Lucy and Jamie going back in time to save Sara and George (as well as Tom) that Sara and Tom live long enough to have offspring. So where did Lucy and Jamie come from initially in order to be able to go back in time and create the conditions so that they will be born? This is almost a single nonbranching, static timeline, except for the fact that initially, Sara, Georgie, and Tom did die (as evinced by what Lucy and Jamie see and hear in the graveyar), so Lucy and Jamie did change things. I think we need a new name for it, perhaps the grandchild paradox.[/spoiler]

As in the The Ghosts, which formed the basis for the film, a mysterious Mr. Blunden arranges for a widow and her children to move to an old English house while the rightful heir to the house is tracked down. But in the film, young Lucy and Jamie are in 1918 rather than the 1960s, and the “ghost children” are from 1818 rather than the 1860s. Nevertheless, Lucy, Jamie, Sara, George, and Tom all have the same adventure in the past along with a cool Grandchild Paradox.