In a luxuriously designed New York apartment, three bachelors live with different careers and different women, sometimes a revolving door of them. It's a good life for them and good careers, with Peter (TOM SELLECK) an architect, Michael (STEVE GUTTENBERG) a cartoonist, and Jack (TED DANSON) an actor headed to Turkey to work on a TV movie.
While Jack is in Turkey, the lives of Peter and Michael change drastically when they find a "package" on their doorstep that Jack told them about from the airport, instructing them not to let anybody know about it because "it's a delicate matter." The "package" turns out to be a baby in a bassinet, Jack's baby with a woman named Sylvia who leaves a note telling him that she can't deal with raising a baby right now and asking him to take care of the girl, named Mary.
While they struggle to learn how to take care of a baby, it turns out that the "package" Jack was talking about was related to a favor his friend, a TV commercial director, asked him to do. And that was to keep the package -- which turns out to be heroin that's to be given to whoever comes to pick it up a few days later -- with him (a subplot is introduced where the baby is erroneously thought to be the package to be given).
Later, Jack comes home and it's time for him to take on the responsibility of being a father, and all three must contend with that as well as the drug dealers, including Vince (PAUL GUILFOYLE), seeking the heroin.