The Time Travelers Wife by Audrey Niffenegger

The Time Traveler's Wife tells the intruiging story of Clare and Henry, who meet when Claire is 6 and Henry is 36 but marry when Claire is 20 and Henry 28. It describes in dramatic detail, their unusual meeting, and their lives together and not. Their story is full of up and downs - Clare can never be sure when Henry will disappear next, where to, or when he will come back. This adds a certain fleetingness and intensity to their relationship, particularily the earlier parts. As the book continues, it adds more flesh and detail to the two central characters; their friends, family, and relationships before and after they met each other. This ensures that the characters are well developed and described - not just reflections of each other.