In the aftermath of World War II, a writer forms an unexpected bond with the residents of Guernsey Island when she decides to write a book about their experiences during the war. Then she learns the secret they are afraid to reveal.

After being unexpectedly widowed, respectable and reserved housewife Grace Trevethyn (Brenda Blethyn) discovers that her late husband ran up significant debts and left her facing foreclosure and numerous repossessions. Well liked around Port Isaac, the coastal fishing town she lives in, Grace is given emotional support by the town's inhabitants, particularly her loyal, cannabis (drug)-smoking gardener Matthew Stewart (Craig Ferguson), his girlfriend and the town's fisherwoman Nicky (Valerie Edmond), and their friend Dr Martin Bamford (Martin Clunes). Despite wanting to help Grace, none of the residents are able to find a way to get her out of her dire situation.