Why actor Matthew Gray Gubler is dressed in a monster suit

'Criminal Minds' star Matthew Gray Gubler on the show winding down after 15 seasons and why he's turning his skill to creating a children's book

NEW YORK -- You have to hand it to actor Matthew Gray Gubler: When he goes, he goes all-in.

That's whether he's chasing serial killers on CBS' "Criminal Minds" or putting the word out about his new children's book.

To publicize "Rumple Buttercup: A Story of Bananas, Belonging and Being Yourself," Gubler donned a full-body costume of his character, a peculiar green monster who hides because he fears he's weird.

The story centers on the lonely Rumple Buttercup, who hides from the world because he has crooked teeth, three hairs and an asymmetrical body.

Gubler says he wrote the "book for anyone that feels like they don't quite fit in."