Killian Delaney and Declan Murphy have been best friends since the crib, brought together by their love of baseball — and, more importantly, the Boston Red Sox. The summer after they graduate college, Declan proposes to Killian that they both move back to their hometown for the last summer before they become 'grown-ups,' spurring a chain of events that brings to light feelings Killian didn't know existed between them. When a career-threatening injury poses an obstacle to Declan's big league dreams, Killian must decide where she stands not only in Declan's professional career, but in his heart.