Every Monday, 49-year-old Ellie looks after her grandson Josh. She loves him more than anyone else in the world. The only thing that can mar her happiness is her husband's affair. But he swears it's over now, and Ellie has decided to be thankful for what she's got.

Then one day, while she's looking after Josh, her husband gets a call from that woman. And just for a moment, Ellie takes her eyes off her grandson. What happens next will change her life forever.

Because Ellie is hiding something in her past. And what looks like an accident could start to look like murder...