Jane Lee (Anna Maxwell Martin) discovers her mother Philomena (Judy Dench) fell pregnant as a teenager in 1952 Ireland and was forced to give up the baby.
Jane pitches the story to former Labour advisor turned BBC journalist Martin Sixsmith (Steve Coogan), who initially scoffs at the suggestion he should pen an article about it.
After a reality check from his wife Kate (Simone Lahbib), Martin agrees to help Philomena track down her boy.
Martin takes Philomena to Washington DC to sift through official documents, hoping for a breakthrough to reunite her with the son she never wanted to give up.
Tears flow as the heroine discovers the fate of her boy, seizing upon every bit of information as if she had just won the lottery.