Graham Masterton 
Blood Sisters [EPUB ebook] 

Katie Maguire never thought Ireland’s nuns would need her protection… In a nursing home on the outskirts of Cork, an elderly nun has been suffocated in her sleep. It looks like a mercy-killing until another sister from the same convent is found floating in the Glashaboy river. The nuns were good women, doing God’s work. Why would anyone want to kill them? But then a child’s skull is unearthed in the garden of the nuns’ convent, and DS Katie Maguire discovers a fifty-year-old secret that just might lead her to the killer… if the killer doesn’t find her first.