The Chain / Adrian McKinty.

"The morning starts like any other. Rachel Klein drops her daughter, Kylie, at the bus stop and heads into her day. But then a phone call changes everything. A woman has Kylie bound and gagged in her back seat, and the only way Rachel will ever see her again is if she pays a ransom - and kidnaps another child. The caller is a mother herself, whose son has also been abducted, and if Rachel doesn't do exactly as she's told, both children will die. Rachel is now part of a terrifying scheme - The Chain. The rules are simple: find the money, find your victim, and then commit a horrible act you'd have thought yourself incapable of just 24 hours ago. Rachel is an ordinary woman, but over the coming days she will be pushed beyond ordinary limits to save her daughter. What the anonymous masterminds behind The Chain know is that parents will do anything for their children. But what they don't know is that they may have met their match. Can Rachel be the one person to finally break The Chain?"--Publisher description.