The night before her wedding, Gwen (Eve Myles) is bitten by a shape-shifting alien. Jack (John Barrowman) kills the alien, but Gwen wakes up pregnant. Jack and Owen (Burn Gorman) arrive to examine her and talk her out of getting married. Her boyfriend Rhys (Kai Owen) wants her to cancel the wedding too, but she insists on getting married and they try to sell the pregnancy as natural. Tosh (Naoko Mori) comes by with a better fitting dress.

At the Torchwood Hub, Owen learns that the alien who impregnated her is a Nostrovite—a carnivorous shapeshifter. They hunt in pairs and mate for life. The eggs are transferred to a host body until they hatch, then the female kills the host. At the wedding, the female alien (Colette Brown) kills and devours a wedding guest. Others are captured and kept for later feeding. Jack demands the wedding be halted. The half-eaten corpse is discovered. The alien escapes through a window.

The alien takes the shape of the groom’s mother Brenda (Nerys Hughes) in the garden. The real Brenda is accused of being an alien but is identified by her perfume. The alien holds Gwen’s mother Mary (Sharon Morgan), demanding her child. Gwen pulls a gun out of her flower bouquet and shoots at the creature. The alien takes the form of Jack. Owen shoots it. The Nostrovite tries to attack Owen but is repelled by the fact that he is dead. Owen has explained to Rhys how to remove the fetus with a singularity scalpel, and he tries to do so in a barn. But the alien attacks Rhys, who tries to defend himself with a chainsaw that doesn’t work. Jack finally kills the alien. The wedding goes on, but all the guests fall asleep at the reception because Jack gave them amnesia pills. Refusing to do so herself because she wants no more secrets from Rhys, Gwen talks of the honeymoon. Back in the Hub, Jack looks at a picture of himself and an unidentified bride at their wedding.

The whole thing was written like a comic soap opera. It was quite controversial, hated by some, loved by others. It was Eve Myles’s idea to eat pickles when pregnant, though she hated them.