Princess Celestia and the Summer of Royal Waves - My Little Pony: The Princess Collection Book 1 (Unabridged‪)‬

Princess Celestia travels to a distant land to help an old friend bring the magic back to her homeland.

When anypony asks Princess Celestia for help, she is more than happy to be of service. So when Duchess Diamond Waves says she is in desperate need of assistance, the wise leader of Equestria clears her schedule.

Arriving at Monacolt Magic Academy, Celestia notices that her dear old friend seems to have lost her sparkle. Diamond Waves confides that her beautiful city by the sea is on the brink of disaster and, having failed their exams, none of her pupils are prepared for what lies ahead. Diamond Waves says her colts and fillies are lacking focus, but that doesn't seem to be the case. When Celestia meets her summer school students, she is shocked to be greeted by a class full of very serious colts and fillies.

What can Princess Celestia do to bring the magic back to Monacolt?