While their fighting parents (Clare Dunne and Michael Socha) desperately search for them, runaways Finn (Roman Griffin Davis) and his live-wire younger brother Charlie (Dexter Sol Ansell) embark on an epic adventure from Yorkshire, over land and sea, to the Wild West coast of Ireland. With the free-spirited busker Cate (Maisie Williams), helping the young boys along the way, their destination is Dingle, County Kerry and their estranged, beloved grandfather (Bill Nighy), who their parents have not spoken to since the fateful events of the previous summer.