‘Room’.
It starts with Jack, who lives with his mother in Room (pretty much just a shed with a small kitchen, bathtub, wardrobe, bed, TV). It’s all he’s ever known, and Jack believes that only Room and the things it contains (including himself and his mother) are "real." Once Jack turns five, his mum starts to let him know the truth, and how they got there.
I read the book (by Emma Donoghue) so thought I would prepared. I was not prepared. Eyes leaking (damn onions), lump in throat etc. Really well done, and the acting by Jack and 'Ma' was brilliant.