Circles Within Circles - Prairie Magic, #1

Mary never believed the rumors about her mother being a witch, but when a mirror inexplicably connects her to her twin brother Michael, stationed half a world away on a WWI battlefield, she reconsiders. To protect him from a battle he has reason to believe will be his last, Mary sets out to uncover any magic left on her isolated farm. The incubus Cairn wakes from centuries of banishment to a cramped basement and a sensual, albeit surprised, woman.
Perhaps she didn't intend to summon him, but since she did, perhaps he could help. for a price.