Content Warning: This section of the guide includes discussion of death.

The Summer Pact that the three surviving friends make is a symbol of the bonds of friendship that draw them together. The name of the season that promises warmth and the height of the growing season lends an optimistic tone to the agreement, though it is also the name of the friend they lost and whose memory they honor. The three muse in one discussion that Summer was their “sun,” in some ways the center of their group; she held them together as a foursome, even though they all had individual bonds with one another. Their commitment to each other becomes, then, not only a demonstration of loyalty and the substance of a promise but also another way to honor Summer: They stay together in the way they imagine she would have wanted.

The way in which the Summer Pact evolves throughout the novel reflects the ways the bonds among the group deepen. The pact that they first make a year after Summer’s death is a promise on the part of each to reach out to one another when they need help. The gravity with which they view this commitment is demonstrated when both Lainey and Tyson give up their career prospects to visit Hannah in person and provide emotional support. As they bond in Capri and experience the island that Summer was curious about, the friends agree that fulfilling this commitment has had a positive impact on all of them. In the Epilogue, when Tyson adds a line to the Summer Pact proposing marriage to Lainey, he confirms the bonds that hold the friends together and acknowledges how they have deepened into love.