Dublin, Ireland, 1881. Isobel Fitzgerald's mother, Martha, marries solicitor James Ellison but an unexpected guest overshadows their wedding day. Martha's father is dying and he is determined to clear his conscience before it is too late. Lewis Greene's confession ensures the Ellisons' expectation of a quiet married life is gone and that Isobel's elder brother, Alfie Stevens, will be the recipient of an unwelcome inheritance.

When a bewildering engagement notice is published in The Irish Times, the name of one of the persons concerned sends Will and Isobel on a race against time across Dublin and forces them to break a promise and reveal a closely guarded secret.