In And Baby Makes Seven, Ruth, Peter and Anna are having a baby. Ruth and Anna are lovers and Peter is gay, but all three want a child.

So one night, Anna tells Peter fantasies of Greek sailors, Nubian slave boys, and English schoolboys. They make love and now Anna is pregnant.

This slightly unusual family, however, already has three children: Cecil, Henry, and Orphan. Cecil is a nine-year-old solemn pedant, Henry is a manic pouting tease, and Orphan has problems interacting socially because he was raised by wild dogs. Anna, Peter, and Ruth rescued Orphan after they found him chasing a bus.

All three boys are disturbed and confused by the idea of another sibling. Unfortunately, conventional advice won't help because Cecil, Henry, and Orphan are not real.

In the sheltered privacy of their house, Ruth pretends to be Henry and Orphan while Anna slips into the persona of Cecil. As Orphan, Ruth snarls, bites, crouches, and whines in broken, stuttering words. In this imaginary world, only Peter remains an adult, Uncle Peter.

As the play progresses, the three children usurp Anna and Ruth until the two women are struggling to control their creations. The three boys begin to gain an independence of thought and desire, separate from Anna and Ruth's sane selves until Anna and Ruth decide the three must die.