7月4日，布鲁克林大桥，一枚抛掷落地的硬币，绿色通道以及黄色通道。
年轻夫妇凯特（琳恩·柯林斯 Lynn Collins 饰）和鲍比（约瑟夫·高登-莱维特 Joseph Gordon-Levitt 饰）深深相恋，然而当他们来到布鲁克林大桥上时，却将彼此的命运交托于一枚小小的硬币之上。于是7月4日这个看似极为普通的一天，对二人来说变得意义非常。当硬币掷地，凯特与鲍比向着两个相反的方向迅速奔跑，而他们的未来，无人知晓。
现实立刻被分割成两条平行时空。在绿色通道中，凯特和鲍比来到了凯特在布鲁克林的家中，度过了宁静而幸福的一天；而在黄色通道中，二人却莫名其妙的来到危机重重的曼哈顿，卷入一场生死攸关的抢劫案中，濒临绝境。

Writer and teacher Iris finds her comfortable, solitary New York life thrown into disarray after her closest friend and mentor bequeaths her his beloved 150 lb. Great Dane. The regal yet intractable beast, named Apollo, immediately creates practical problems for Iris, from furniture destruction to eviction notices, as well as more existential ones. Yet as Iris finds herself unexpectedly bonding with Apollo, she begins to come to terms with her past, and her own creative inner life in this story of healing, love, and friendship.