The role of family as an element of identity and the instability created by the loss of (or fear of losing) them proves a key theme throughout The Secret Keeper, uniting each of the story’s central characters. While all four of the main protagonists have suffered from losing family in some way, creating or preserving a family is also the goal that all four major characters strive for. Jimmy and Dolly plan to marry and live by the seaside. Vivien longs for a family she believes will be denied her in her cruel marriage, but when she becomes Dorothy Smitham, and later Dorothy Nicolson, she leaps at the chance to build a family of her own. While Laurel acknowledges that they can be exasperating at times, she hopes to preserve her family and her relationships with her siblings even as she uncovers her mother’s secret. Laurel seeks confirmation, through understanding her mother’s motive for murder, that the family of her childhood was built on foundations of love.

All three of the characters in the World War II timeline have been marked by losing their family at an early age, which creates a deep longing for family in each of them as adults.