Nate the Great and the Tardy Tortoise by Marjorie Weinman Sharmat and Craig Sharmat illustrated by Marc Simont

My first grader read this book to himself.
This is his review-
"I liked it because when he was trying to solve the case, Claude had another case for him to solve.  Claude lost his sock.   This is a summary of the story:  Nate the Great went outside and saw nibbles on his flowers.  He looked around and found a tortoise nibbling the flowers.  Sludge gave a clue.  He was sniffing a lot.  Then Nate the Great knew he should follow the trail of the nibbled flowers."
PS He does find Claude's sock!! :-)
-Borrowed from the library.
*Highly recommend.
Guided Reading Level: K (end of 1st grade/beginning of 2nd grade)