Newborn Peter (Levi Miller) is left on the steps of a London orphanage with a mysterious pan flute pendant by his mother Mary (Amanda Seyfried). Years later during World War II, upon learning that the abusive Mother Barnabas (Kathy Burke) is hoarding food for herself, Peter and his best friend Nibs (Lewis MacDougall) are caught trying to steal the food for the orphans. In the process, they find a letter written to Peter by his mother, declaring her love and assuring him they will meet again "in this world or another".