Baobhan Sith

Weary from rebuilding the Hellsing Organization's army from the Valentine Brothers' attack, as well as being dismissed from a vampire attack by MI-5 (and bothered by an ominous premonition from Alucard), Sir Integra Wingates Hellsing received a surprise visit from Laura, her sister living in the Essex area. The visit was friendly but soon unusual events were occurring: Seras Victoria was being restrained by Walter, Alucard has his first encounter with the masochistic vampire Incognito, and Integra herself was unusually fatigued.

She then realized all too late the sad truth – she was an only child, and the woman claming to be her sister was in fact a vampiric assassin. "Laura Hellsing" is in reality a Baobhan Sith – a Celtic vampire often referred to as "the White Woman". Baobhan Sith often wear long green gowns, and have been known to use hypnotism to ensnare its victims. This particular one had stabbed Integra in the stomach before drawing her blood... then Alucard (because of Incognito's boasting) realized what was happening, interrupted and slew the beast before Integra was killed. And as a result, Walter was released from the enchantment that forced him to restrain Seras and both raced to Integra's aid.

However, because she was bitten, Integra nearly kills herself by stabbing herself in the neck to draw out the creature's taint from her body. She was later saved in a hastily-arranged operation by Dr. Trevelyan soon afterward. (source: Absolute Anime)