Warning: Extreme

She's been your maid for a long time — warm, maternal, impossibly good at her job. But at night she slips out in plain clothes, and she comes home with a new keepsake. Sarah has tortured and killed seventeen people in the last year, and she's been hiding it right under your roof. Now she's decided you're next. Can you catch her before she catches you — and if you do, how hard will she fight?

Slow burn, unless you start looking for clues yourself.