"Working for the FBI, cryptanalyst and agoraphobe Salem Wiley vows never to return to the conspiratorial underworld her mother revealed to her. Until fieldwork draws Salem to an Ireland farm where a curious discovery has been unearthed: a near-perfect replica of Stonehenge in miniature--except for one extra stone engraved with the word mercy. When seven-year-old Mercy Mayfair, a child in Salem's family's care, is kidnapped, Salem knows it's more than...