Josie Morrow and Lina Braid are the best of friends. But although Josie has an "understanding" with Agnus, Lina's brother, her mother has far more grandiose plans than for her to marry a local boy. She sees civil engineer Duncan Guthrie, a lodger in their Queensferry boarding house, as a much better catch, However, it is Lina who Duncan falls for, forcing her to break her promise to her childhood sweetheart in order to marry him.