Rose Randall Not scary at all. The fact that a child dies, is upsetting, but as you delve deeper, the questions Mack asks, becomes understandable. The answers come, slowly to start off with. But with knowledge, comes understanding. Then no, it is not scary.
This answer contains spoilers… (view spoiler)[I'm only about halfway through, but I would guess the worst is past. It's not scary, per se, but early in the book, a violent crime is committed against a child, which may be tough for some people to stomach. (It's not described in any kind of graphic detail, however.)