John Booker begins a letter to Juliet. He explains that he only reads one book over and over: The Letters of Seneca. Seneca and the Society kept him from the life of a drunk. From 1940-1944, he pretended to be his employer, Lord Tobias Penn-Piers, who fled Guernsey when the Germans bombed it. He doesn't remember much of the night that he, Dawsey, and Elizabeth were stopped after the pig roast, as he was drunk. Booker says that Seneca's book is comprised of letters to imaginary friends telling them how to behave. He says that they're witty and are applicable even in the modern day.
For John, the Society kept him connected to other people so that he couldn't waste his life away drinking alone. With this, the novel again holds up literature as one of the best ways to make friends. However, the fact that Booker only reads one book makes it clear that making friends thanks to books isn't contingent on reading many different things; one book is enough to form a connection.
Booker writes that at the start of the war, Lord Tobias purchased a manor on Guernsey and moved there with his wife. Booker was his valet and supervised the outfitting of the house, including the stocking of the wine cellar. However, as the finishing touches were put on the house, the Germans bombed Guernsey. Lord Tobias took as many of his possessions as possible and left the island. Booker still had the key to the wine cellar, so he stayed.
Like Elizabeth, Booker isn't a Guernsey local but he still managed to become part of a robust and strong community through the Society. This begins to challenge people like Adelaide, who insist that not being a native of Guernsey is a mark against someone and a reason why they're not worthy of consideration.
Booker worked his way through the cellar uninterrupted until September, when Elizabeth and Amelia warned him that the Germans wanted to register all Jews on the island. Elizabeth knew that Booker's mother was Jewish, and she'd come up with a plan: that John impersonate Lord Tobias. Elizabeth even offered to paint John's portrait as a sixteenth century noble to complete the effect. Two weeks later, when the Germans came to try to take control of the house, they bought the act and let him live in the gatekeeper's cottage. Booker had already found friends in the Society by the time he ran out of wine, and the meetings made the occupation bearable. Now, he refuses to read anyone but Seneca and his experience as Lord Tobias has led him to acting.
Once again, Elizabeth shows that she cares deeply for the people on Guernsey regardless of whether or not she's related to them or even knows them well. This indicates that Elizabeth recognizes the humanity of all people, not just those she calls family. Booker suggests that without the Society or wine, he might not have made it through the war. Again, this speaks to the power of the Society's friendships to keep people alive during difficult times.