Secrets, surprises and disappointments all crowd the pages of Eighteenth Summer. Sarah's dear friend, Nancy, must pick up the pieces of a shattered dream and go on with her life. With advice from Sarah she is able to do so. Cousin Marnie must spend the summer tucked away in her grandmother's home. The only person she knows she can trust with her secret is Sarah, the cousin whose feelings she has delighted in hurting every summer. A tall stranger singles Sarah out from a group of friends at the Fourth of July parade. During their brief encounter Sarah once more receives a proposal of marriage. Sarah receives a letter from Ohio and rushes to read its contents. She is heartbroken to learn her friend of six years is in love. Words in the letter like, 'special' and 'friend' do nothing to mend her wounded heart.