At Torchwood 's Cardiff headquarters , Owen determine from an autopsy that the alien that impregnated Gwen is a Nostrovite , a race of carnivorous shape shifters who hunt in pairs and mate for life . He tell Jack that after fertilisation , the female transfers her eggs to the male who plant them in a host body until they are ready to hatch . Later , the female kill the host to release the offspring . At the wedding venue , the female Nostrovite ( Colette Brown ) murders and partly devour wedding guest Mervyn . Toshiko investigate along with Rhys ' best man " Banana Boat " ( Jonathan Lewis Owen ) and they are subsequently captured by the alien , who intend to feed on them later . As Gwen and Rhys prepare to say their wedding vows , Jack run up the aisle and demand that the wedding be halted . Owen and Ianto ( Gareth David @-@ Lloyd ) free Toshiko but the half @-@ eaten corpse of Mervyn is discovered by his wife , a bridesmaid , who alert the entire wedding party to the murder . The Nostrovite reveal herself and is chased away by Jack , escaping through a window .