The Banshee is a villainess in the TV show Strange. She is based on the original Banshee in folklore, and the Banshee can contaminate human society by bringing an infernal plague with her. In fact she desires to doom people to Hell by making them die of plague before summoning the Costa Burra (Death Coach) to take them to Hell.
The Banshee was born as a human peasant child in 15th century Ireland in the year 1470. Nine years later, she was among the many who were struck down by a plague which had engulfed her village and killing both her parents. The Death Coach arrived and knowing it was for her, and knowing that it couldn't return to Hell empty, she made a deal with the coachman. He agreed that she could live, but only as his emissary on earth, sacrificing her soul and becoming a Banshee who would spread the disease, preying on plague ridden villages summoning the coach for the dying, the sick and the elderly with her demonic cries to collect the souls of the plague victims.
She did this over the next four centuries across Ireland (and presumably elsewhere) until 1908 when she reached Late Victorian England, she pretended to be orphaned and got adopted by a rich family. From there on, she seemed to live amicably with her adopted sister Pandora Otterman. Nonetheless, the Banshee was still planning to spread the plague, and call her fellow companion, the Costa Burra, the death coach, to harvest the souls of the deceased. During that time, she began to notice the heavy handed abuse that was dealt out to Pandora by Bishop Otterman, her adopted father.
The Banshee successfully did so, causing countless deaths across the city, wherass many victim bodies were reported to have mysteriously vanished, having been taken to Hell by the Costa Burra at the Banshee's behest. To prevent suspicion from being aroused, she herself pretended to be stricken with the illness and lay bed ridden. However, when nobody was looking or listening, she called to the Death Coach, summoning it and taking her adopted father to Hell, having had enough of the ill-treatment he delivered to Pandora.
The disappearance was not lost on visiting Irish Dean Patrick McGrath who, being very much aware of the Banshee's dark reputation and legend, realised that she resided in the house, having seen the Costa Burra's track marks on the ground and Pandora standing nearby. His suspicion immediately fell on Pandora Otterman and in an attempt to solve the problem himself, sealed Pandora in a wall cavity, burying her alive. The Banshee, knowing that this was her fault was devastated, because her adopted sister was the only human she had ever cared for. The Banshee had begun to get a friendship with the girl and she was struck by sadness and guilt when her actions had resulted in Pandora's death. As a result, the Banshee lived in remorse the rest of her life, abandoning her ability in the Coach summoning as well as the spread of pestilence, allowing herself to age naturally, attempting to live a normal life.
Eventually in 2003 the Banshee, who as Miss Otterman was a very old woman, was asked by a Medical Postgraduate Researcher, who was researching the plague she spread as the official story was that Bishop Otterman had died of the plague, his body being sealed in a tomb. She refused. However, suspecting that he might disturb Pandora's body, she followed him to the Cathedral, calling the Costa Burra and taking him to Hell.
With John Strange
John Strange, a disgraced priest, had heard of the plague and the mystery surrounding Bishop Otterman's tomb. His researcher Toby discovered a scripture that mentioned a "great evil" being disturbed if the tomb was ever opened but no clear answers as to what. Strange arrived at the Cathedral himself but only discovered track marks and no sign of the Medical Researcher, realising "something had turned up to greet him". Finding the demon and discovering it's identity was a difficult matter. He tracked down an old woman (the Banshee) who knew of the last victim who had died of the plague. She seemed very introverted and liked quiet life but explained to him that Bishop Otterman's tomb was empty. Strange didn't suspect her, and went away to ponder who and what the demon was.
Soon however, Strange was met by Irish taxi driver Liam McGrath, the great-great grandson of Dean McGrath who had followed the researcher from Ireland in fear that he would unleash the plague and the demon. Knowing the full story, Liam provided Strange with information and the full backstory on the Banshee, an Irish demon, whose cries called the Costa Burra death coach to Earth from Hell. Once there, the coach could not return empty-handed. Strange realized the demon was the Banshee and suspected that the Medical Researcher had released it from it's tomb by mistake.
Strange was confronted by Canon Black and the elderly Banshee, revealing that the tomb contained nothing more than Pandora's corpse. On Canon Black's departure, Strange confronted the Banshee, having discovered her adoption papers as well as her true identity. At that, the Banshee revealed her true nature, Strange and Jude, his assistant, being frozen in place as her cries summoned the Coach. She promised to take them both to Hell and called the Costa Burra coach which galloped out of it's fires, driven by a black-robed headless horseman.
The Banshee revealed to Strange and Jude that she had sent the researcher to hell. The two of them could not escape as they had been frozen to the spot. Strange, empathising with her situation reminded the Banshee of her crushing, weary loneliness. At that, the Banshee, remembering her grief for her adopted sister, decided to end her own life. Climbing on the death coach, she bid John Strange goodbye thanked both of them for allowing her the opportunity of closure. The coach departed and the Banshee screamed as the fires of Hell burned away her mortal body and she exploded in a ball of flame. The Costa Burra coach rode back into Hell, taking the turbulent remains of the Banshee with it.