This is a jukugo word that uses the on'yomi for both kanji. You haven't learned this reading for 怪 yet, so here's a mnemonic to help you:
I get so suspicious about my injury that all my 毛 (け) stands on end.
Yesterday, my daughter was injured at school.
Even monsters get sick and injured.
I heard that the cause of that child's serious injury was a banana peel.