I See You by Clare Mackintosh

London is wired with surveillance cameras for public safety. But aside from the police, who else is using those cameras--and for what reason? In the extremely unsettling I See You, someone is using the cameras to watch women on the subway (the Tube) going to and from work every day and making note of their routines. Then they're selling the information to anonymous men who might want to "meet" those women. Middle-age mom Zoe Walker realizes she might be in their sights when her picture pops up on an ad for a dating website she's never heard of.  She finds one lady cop--whose own sister had been raped years earlier--who takes her seriously. Zoe becomes increasingly anxious as bad things keep happening to other women whose pictures popped up on the website's ads. It all leads to a nail-biting conclusion and some good surprise twists.