Kate and Geoff Mercer are planning to celebrate their 45th wedding anniversary with dozens of friends in a community hall near Norwich. A week before the party, Geoff receives a letter that clearly troubles him, though he tries to hide it from Kate. He eventually tells her that the body of Katya, his first great love who disappeared fifty years earlier in the Alps, has been found in a melting glacier. Geoff begins acting strangely, and Kate starts to question who the man she married so long ago really is.