The epilogue in And Then There Were None is an epilogue written from the point of view of Detective-Superintendent Edward R. Blore, the sole survivor of the events at Indian Island.
Detective Blore is convinced that, although the eight murders that he investigated were solved, there is still someone out there, who is responsible for them. He believes that it is his, or someone else's, duty to step in and bring the person responsible for the murders to justice.
The epilogue further reveals that the case will remain unsolved, as Blore turns his back on the investigation and returns to London, never to solve the mystery. Despite his best intentions, Blore accepts that he will never find the person who orchestrated the murders and it is a case that will remain unsolved in spite of his efforts.
The epilogue serves as an ending to the novel, with the reader coming to terms with the fact that justice will never be served and that no one will ever know who was behind the murders. This leaves a lingering sense of unease and provokes the reader to consider whether justice should truly go unserved in such a situation.
