The Eleventh Hour (1989) is yet another wonderfully written and spectacularly illustrated book by Graeme Base. From the jacket:
When Horace the elephant turns eleven, he celebrates in style by inviting his friends to a splendid party. Fine music, games, and the promise of a magnificent feast prepared by Horace himself (everyone knows elephants are the world's best cooks!) make this costume gala a most special event. But little does Horace know that when the partygoers gather for the banquet, a curious mystery will be revealed. None of the eleven animals is above suspicion when the clock strikes The Eleventh Hour!
The rhyming text and detailed illustrations provide clues to solve the mystery. The back of the book holds a sealed section labeled Top Secret, which (if you break the seal) will reveal not only the solution, but detailed explanations of all of the clues and puzzles.

The guests are