The Hidden is the thirty-ninth book in the Animorphs

Animorphs

Animorphs is an English language science fiction series of young adult books written by K. A. Applegate and published by Scholastic. Five humans, Jake, Marco, Cassie, Rachel, and Tobias, and one alien, Aximili-Esgarrouth-Isthill , obtain the ability to morph into any animal they touch. They name...

series. It was ghostwritten

Ghostwriter

A ghostwriter is a professional writer who is paid to write books, articles, stories, reports, or other texts that are officially credited to another person. Celebrities, executives, and political leaders often hire ghostwriters to draft or edit autobiographies, magazine articles, or other written...

 by Laura Battyanyi-Wiess (as K. A. Applegate). It is narrated by Cassie

Cassie (Animorphs)

Cassie is a fictional character from the sci-fi book series Animorphs, written by K. A. Applegate. Her last name is never mentioned, although she referred to it as being "nice" in The Secret.-Biography:...

.

Plot summary

The Yeerks repair a downed Helmacron ship and use its sensors to track the Escafil Device

Escafil device

The Escafil device is a fictional technological apparatus from K.A. Applegate's popular children's book series Animorphs. It is the proper name for the "Andalite morphing cube", a device that when operated gives the user the ability to 'acquire' a copy of DNA patterns from any animal that physical...

 and the Animorphs morphing abilities. Cassie is forced to relocate the Escafil Device

Escafil device

The Escafil device is a fictional technological apparatus from K.A. Applegate's popular children's book series Animorphs. It is the proper name for the "Andalite morphing cube", a device that when operated gives the user the ability to 'acquire' a copy of DNA patterns from any animal that physical...

. During the process, a Cape buffalo and an ant inadvertently gain the morphing ability. The buffalo morphs Chapman and begins to learn speech, and the ant morphs Cassie. Cassie kills the ant when it demorphs, and near the end of the book the buffalo is killed by a Dracon beam. However, the Animorphs come up with a plan similar to Megamorphs #1, in which Cassie morphs a humpback whale in midair to destroy the helicopter carrying the Helmacron ship.

Morphs

Morpher	Morphs Acquired	Morphs Used
Jake Jake Berenson Jake Berenson is a fictional character and one of the main protagonists from the science-fiction book series Animorphs, written by K. A. Applegate. Until the penultimate book of the series, his last name was never revealed, and he was known only as Jake...		Wolf, Dolphin, Fly, Seagull, Siberian Tiger
Rachel Rachel (Animorphs) Rachel is a fictional character from the sci-fi book series Animorphs. Her full name is never explicitly mentioned in the books, but her relation to her cousin Jake Berenson through their fathers makes it most likely to be Rachel Berenson, if it was never changed or hyphenated.-Biography:Before the...		Wolf, Dolphin, Fly, Seagull, Grizzly Bear
Tobias Tobias (Animorphs) Tobias is a fictional character from the sci-fi book series Animorphs written by K.A. Applegate. His surname is never mentioned, but had the Ellimist not altered time in order to take his father, Elfangor-Sirinial-Shamtul, back to his old life, his full name would have been Tobias Fangor, the...		Dolphin, Fly, Wolf
Cassie Cassie (Animorphs) Cassie is a fictional character from the sci-fi book series Animorphs, written by K. A. Applegate. Her last name is never mentioned, although she referred to it as being "nice" in The Secret.-Biography:...	Cape buffalo	Cape buffalo, Humpback Whale, Seagull, Wolf
Marco Marco (Animorphs) Marco is a fictional character from the sci-fi book series, Animorphs, written by K. A. Applegate. His last name is never mentioned.-Biography:...		Wolf, Dolphin, Fly, Seagull, Gorilla
Ax Aximili-Esgarrouth-Isthill Aximili-Esgarrouth-Isthill is a fictional character from the sci-fi book series Animorphs.-Biography:Aximili is a young Andalite who becomes stranded on Earth when the Andalite Dome Ship GalaxyTree is shot down by Yeerk fighters...		Dolphin, Fly,
Visser Three Visser Three Visser Three, born as Esplin 9466 Primary and later known as Visser One, is a fictional character and the main antagonist of the sci-fi book series Animorphs, written by K.A. Applegate. He is the leader of the Yeerk forces on Earth, having inherited the planet from Edriss 562, who was Visser One at...
Buffa-human	Human (Chapman), Andalite (Alloran-Semitur-Corrass Alloran-Semitur-Corrass Alloran-Semitur-Corrass is a fictional character in the Animorphs series by K. A. Applegate. He is the host body of Visser Three, a high-ranking Yeerk and the primary antagonist of the series.-Character history:... )	Human (Chapman), Andalite (Alloran-Semitur-Corrass)
Ant	Human (Cassie)	Human (Cassie)

Trivia

• The cover quote is, "To morph or not to morph? That is the question..."
• The inside cover quote is, "Where the buffalo roam..."