Robert (RUPERT EVERETT), a Los Angeles gardener, and Abbie (MADONNA), a yoga instructor, have been best friends for years and would seem to make a perfect couple. The only problem is, he's gay and Abbie's sworn off men after her latest boyfriend, Kevin (MICHAEL VARTAN), leaves her.
When a mutual friend of theirs dies, the two spend more time together, and after a few too many drinks, they end up sleeping together. The next day, neither can believe what they did and their friendship becomes strained. That is, until Abbie realizes she's pregnant and asks Robert to be the baby's father. He agrees, but only under the condition that he not become her husband and that the two, while living together as an unconventional family, will be free to date whomever they choose.
While his father, Richard (JOSEF SOMMER), and gay friend David (NEIL PATRICK HARRIS), think it's a bad idea, his mother, Helen (LYNN REDGRAVE), encourages him to embrace fatherhood. The arrangement seems to work well, but several years after the birth of their son, Sam (MALCOLM STUMPF), the two feel the strain of seeing the other dating someone else.
That issue comes to a head when Abbie meets Ben (BENJAMIN BRATT), an investment banker, and the two become quite serious. As their relationship intensifies, the three try to deal with their unique family structure and figure out what's best for Sam.