In her thirties, Kassie Larson is single, has not found love yet, and decides she wants to have a baby. Despite the objections of her long-time best friend Wally Mars, she chooses to do so alone because she cannot wait any longer. She also wants a face-to-face sperm donor, disdaining using a sperm bank.
Wally suggests he be the donor, but Kassie believes he is too neurotic, pessimistic, and self-absorbed. Since they are best friends, she thinks “That would be weird.” He has always had feelings for Kassie, and they dated six years ago. His friend Leonard points out he missed his chance when she relegated him to the “friend zone.”
Kassie selects Roland Nilson as her sperm donor; he is a handsome, charming, and married assistant professor at Columbia University. She organizes an “insemination party”, where Wally meets Roland and takes an instant dislike to him. Roland produces his sperm in the bathroom, leaving it in a sample cup. Wally uses the bathroom and sees the sample. Drunk, he plays with the cup and accidentally spills it into the sink. Panicking, he replaces the sperm with his own.
The next day at work, still hungover, Wally remembers nothing. The insemination is successful and Kassie becomes pregnant. He is upset when she says that she is returning to her childhood hometown in Minnesota, as she thinks it would be a better place to raise a child than New York City. Kassie leaves, and Wally sinks into a dreary period.
Seven years later, Kassie returns to New York with Sebastian, her precocious and neurotic six-year-old. She wants to reconnect with Wally and eagerly introduces her boy to him. Wally eventually bonds with Sebastian. Roland is in the picture as he got divorced, and Kassie has started dating him. She believes he is Sebastian’s biological father and the relationship might work.
Wally notices the strong similarities between him and Sebastian and realizes the result of the switch seven years earlier. Just before Roland proposes to Kassie, Wally reveals to her that Sebastian is his biological son, and he loves her. Shocked and angry about the switch, she rejects him.
After some time passes, Wally finds Kassie waiting for him one day after he leaves work. She says that Sebastian really misses and needs him. He misses and needs Sebastian, too. Kassie says she is no longer with Roland and has realized she loves Wally, so he proposes. The final scene shows a happily married Wally and Kassie giving Sebastian an eighth birthday party.
Watch The Switch to experience the heartwarming journey of friendship, parenthood, and love unfold before your eyes.