Peter (Levi Miller) is a young boy who is left as a baby on the steps of an orphanage in London by his mother Mary (Amanda Seyfried), an establishment under the care of Mother Barnabas (Kathy Burke). Several years later, during World War II, upon learning that she is hoarding food for herself, Peter and his best friend Nibs (Lewis MacDougall) try to steal it to distribute amongst themselves and the other orphans but they are caught. In the process, Peter finds a letter written by his mother, declaring her love and assuring Peter they will meet again "in this world or another.