Princess Celestia and the Summer of Royal Waves

My Little Pony: Princess Celestia and the Summer of Royal Waves by G.M. Berrow is the thirteenth in a series of chapter books published by Little, Brown and Company and the first entry in a four-book miniseries called "The Princess Collection". The story involves Princess Celestia traveling to a distant land to help an old friend.

Sunrise Over Canterlot
The chapter begins by showing in detail Princess Celestia's daily ritual of raising the sun. Princess Luna, seeming more exhausted than usual, then shares with Princess Celestia news from the coast: Apart from a manticore disturbance, a Carcinus—a building-sized species of giant crab—also appeared. Princess Celestia begins to doubt if she should make the journey to Monacolt, whose duchess is facing trouble at her magic academy. Princess Luna, however, encourages her to keep her promise.

The Princesses of Equestria
Princess Celestia worries how the kingdom will fare in her absence, but Princess Luna reveals that she has brought in Twilight Sparkle to help out at Celestia's own school and watch over Canterlot during the day. Princess Celestia instructs Twilight and Luna to send her a letter if necessary with news of Equestria.

A Princess Abroad
Celestia and her Royal Guards fly over the scenic territories surrounding Prance, finally arriving in the breathtaking coastal state of Monacolt. Here she meets her old friend Duchess Diamond Waves, who is visibly worse for wear. The duchess tells Celestia that for the first time in Monacolt's history, the students haven't passed their exams - and this means that none of them are ready for what lies ahead...

Well-Behaved Unicorns
Princess Celestia witnesses the duchess's harsh teaching methods, and soon learns the reason for her friend's dire spirits. The school is home to the Time Glass, an ancient artifact which Celestia thought long destroyed. Diamond Waves explains that the sands of time are about to run out... and when they do, it is said that the ponies of Monacolt will have to protect the borders from a great invasion of beasts.

Lesson Number Fun
Diamond Waves has left for Northern Prance in connection with the impending crisis, and Princess Celestia is left with the duty of preparing her students. The young unicorns seem overworked from the duchess's urgent efforts, and Celestia begins applying her own teaching methods.

The Key to Magic
Princess Celestia's methods begin to meet with success, and the students manage to successfully create the Fire of Friendship.

Out of the Bubble
Celestia takes the students to the ocean shore for a surprise lesson. Some alicorn lore is discussed, as well as Celestia's mane and tail. The princess's lesson begins by instructing the students to enjoy themselves on the beach. Duchess Diamond Waves, however, returns from Northern Prance at this point and passes the shoreline... Feeling overcome by what she perceives as Celestia's betrayal, she leaves too soon to witness the encouraging results of the lesson.

The Good News
Princess Celestia grows increasingly suspicious of the magic of the Time Glass. Something seems off... and despite her hopefulness regarding the unicorns' ability to defend Monacolt, she finds Diamond Waves in dark spirits. Celestia invites the duchess to walk with her to the sea, despite the lack of waves...

Making Waves
Celestia manages to bring some cheer to the duchess's heart, which restores her lost magical abilities - and with them, her power to bring waves to the shores of Monacolt. This is shortlived, however, for the duchess soon gives in to her bitterness and worry over the coming doom. She reveals what she witnessed at the beach, and tells Celestia to leave Monacolt. Princess Celestia's Royal Guard attendants now appear, however, with dire news: There has been a Carcinus attack on Canterlot.

A Letter from Home
Celestia reads over the various reports she has received from Equestria. Despite the other letters being characterized by panic and urging her to return, Twilight's alone claims that she and Princess Luna have the situation under control. Celestia, troubled, debates whether to go or stay - Until a touching event involving one of the Monacolt students helps her make up her mind.

Nighttime Glass
Celestia is determined to save both the land and her friendship with Diamond Waves. As she sleeps, she is plagued by a troubling dream involving the Time Glass - Only for Princess Luna to enter her dream, Carcinus in tow. During their discussion, Celestia learns the truth about the Time Glass, its connection to the griffon King Grover and its former role in griffon society. Princess Celestia now believes that in order to convince the duchess that her students can handle a dangerous situation on their own, they must stage an attack.

Failed Exams
Despite their successes with Celestia, the students are not faring well in their exams. The duchess makes ready to prepare for the prophesized doom, but Celestia urges her to the sea - For the sands of time, she claims, have nearly run out.

Attack on Monacolt
At the seaside, the Carcinus emerges from the ocean. Diamond Waves attempts to shield her students, but they prove themselves capable of defeating the beast on their own. She no longer doubts Celestia.

Wave Good-bye
Princess Celestia prepares to leave Monacolt. The young unicorns are sad to see her go, but Duchess Diamond Waves is restored to her old self. Celestia flies into the sunset, her friendship salvaged and Monacolt's future assured.

Quotes

 * Princess Celestia: Gratias ad solis ortum.


 * Princess Luna: All right, you caught me. I'm planning to transform to Nightmare Moon mode as soon as you leave the border!


 * Twilight Sparkle: What's not fun about speed-reading through the entire Encyclopedia Equestria and then quizzing each other on it?
 * Princess Celestia: You be sure to let me know when you figure it out, Twilight.