Tom, greeting-card writer and hopeless romantic, is caught completely off-guard when his girlfriend, Summer, suddenly dumps him. He reflects on their 500 days together to try to figure out where their love affair went sour, and in doing so, Tom rediscovers his true passions in life.

A father recounts to his children - through a series of flashbacks - the journey he and his four best friends took leading up to him meeting their mother.