Invisible — Tom Lowe

When Sean O'Brien watches a girl darting through traffic to pick up money she dropped, he stops to help. The next time he sees her face it's during a TV newscast. She's vanished. As the case grows cold, Sean can't forget the touching story she shared with him. To find her, he must enter the dark web, infiltrate a global criminal ring, outwit one of the sharpest and most inhuman minds he's ever faced in a battle where the girl's life is reduced to a matter of days.