Enid Blyton 
The Mystery of the Invisible Thief [EPUB ebook] 

“Do you know, ” said Pip, “this is the fourth week of the summer holidays—the fourth week, mind—and we haven’t even heard of a mystery!”
“Haven’t even smelt one, ” agreed Fatty. “Gosh, this sun is hot. Buster, don’t pant so violently—you’re making me feel even hotter!”
Buster crawled into a patch of shade, and lay down with a thump. His tongue hung out as he panted. Bets patted him.
“Poor old Buster! It must be frightful to have to wear a fur coat this weather—one you can’t even unbutton and have hanging open!”
“Don’t suggest such a thing to Buster, ” said Fatty. “He’d look awful.”
“Oh dear—it’s too hot even to laugh, ” said Daisy, picturing Buster trying to undo his coat to leave it open.