Laurie and Alan are thrilled to find out that they'll finally be having a baby, until they discover the unthinkable: the doctor has impregnated Laurie with the wrong man's sperm. Alan is reeling, torn about the new child that's not his and suddenly unsure about any of his commitments. His shock is almost as great as that of Jack, a college junior who suddenly finds out he's a father, and whose identity is discovered as he is juggling finals, his fraternity, a fund shortage, and two girlfriends.