Kayleigh Towne is a beautiful and successful singer-songwriter, and Edwin Sharp is her biggest fan. When she replies to one of his fan letters with 'XO', Edwin is convinced she loves him. Nothing Kayleigh or her lawyers can say persuades him otherwise... Kayleigh's friend Kathryn Dance, a special agent with the California Bureau of Investigation, knows that stalking crimes are not one-off occurrences; and with help from forensic criminalist Lincoln Rhyme, Dance must track him down.