Monster Planet is the third and final novel of David Wellington's Monster trilogy. It takes place twelve years after the events in Monster Island. Sarah, Dekalb's now 20-year-old daughter, fights alongside Ayaan and her squad of female Somali warriors to defend their last remaining settlements from the encroaching undead forces. Meanwhile, a powerful lich from Russia who calls himself "The Tsarevich" leads his army west on an unknown expedition.
Monster Planet provides the following tropes:
- Alternate History: The surviving remants of humanity has reached the 2010s decade but technological progress is severely delayed due to the zombie apocalypse lasting for 12 years.
- After the End: A grim situation for the human race as they get fewer and fewer in the years that followed the initial outbreak.
- And Then John Was a Zombie: Ayaan becomes a lich midway through the novel.
- Apocalypse How: Intially a Class 2 then becomes a Class 6 should Mael have succeeded.
- Big Applesauce: The ruins of New York City is revisited by the protagonists.
- Big Bad: The Tsarevich.
- BFG: The OICW prototype weapon Sarah found on a supply crate in Governor's Island, which she makes her next weapon.
- The zombie werewolf Erasmus attempts to use a Stinger missile agains't Osman's helicopter.
- Bittersweet Ending: As a form of Earn Your Happy Ending, Nilla successfully stops Mael's plans of ending the world and the zombie apocalypse at the cost of her own physical self. However, Dekalb and Ayaan are dead by the end of the novel, leaving Sarah and Osman behind alongside dozens of survivors of the zombie apocalypse. This is in addition to the millions of lives lost in the past 12 years. Though it is assumed what remains of the human race will rebuilt the plant, the ending quote states: "it would be a quiet Earth for the next years to come.
- Call-Back: Aside from Sarah, Ayaan, and Osman, other notable characters return such as Dekalb, Gary, Nilla, and Dick the armless zombie alongside other survivors from Monster Island. Bannerman Clark's zombiefied corpse is also mentioned, still struggling to escape from the helicopter wreckage 12 years on.
- Ayaan then later Sarah and Osman return to New York with Osman happily reuniting with the survivors of Governor's Island after not seeing them for over a decade.
- The Source in Colorado is also revisited.
- Nilla stopping Mael's plans to end the world fulfills her role as the one who could stop the apocalypse as mentioned in Monster Nation.
- The Chosen One: Mael Mag Och chose Sarah to solve his riddle that would have ended apocalypse but Nilla is the one that ultimately ends it.
- Civilization Destroyer: Mael Mag Och was capable of eliminating all life forms on earth, from humans to animals to plants and even simple bacteria.
- Cool Boat: The Finnish Navy submarine Sarah and Osman encounter in which a sole surviving Finnish Navy sailor lets them stay for a while.
- Cosmic Horror Story: A continuation of Monster Island and Monster Nation.
- Curb-Stomp Battle: Sarah's mummy companions are easily defeated by the Tsaverich's forces.
- Demoted to Extra: A zombie Bannerman Clark is still seen stuck on the metallic bar from the helicopter crash in Monster Nation. Ayaan and Nilla leave behind his still-moving corpse as they journey towards the Source.
- Eldritch Location: The realm where Sarah is shown by Nilla. It is shown to be a large boneyard in a lake of blood with a large skull as the moon hovering above it.
- Enemy Mine: Gary, who is the archnemesis of Dekalb and the humans, ends up helping Sarah against the Tsaverich and Mael's forces.
- Revived mummies serve as allies to Sarah since the Tsaverich is also threatening to wipe them off from existence.
- The End of the World as We Know It: Mael came so close to ending all life on Earth had Sarah not convinced Nilla to use her last powers to stop the bogman.
- Evil vs. Evil: Gary Fleck vs. Mael Mag Och, continuing on from Monster Island.
- Face Death with Dignity: Lich!Ayaan prays to Allah (as she is a Muslim) and tells Sarah to shoot her in the head right away. Sarah does so and pays Due to the Dead to her former mentor.
- Festering Fungus: Sarah comes across one released from a lich in the ruins of New York City.
- Greater-Scope Villain: The gods that Mael Mag Och answer to.
- Heroic Sacrifice: Nilla uses the last of her lich powers to put a stop to Mael Mag Och's plans to end the world. This successfully foils the bogman's plans but takes Nilla's life as well.
- Impaled with Extreme Prejudice: Erasmus is killed when a giant skull-crab Gart impales him the werewolf with his gigantic crab legs.
- Karma Houdini: A skull-crab Gary (the main villain of the first novel) ends up surviving throughout the trilogy, though Sarah warns him that he can no longer regenerate and that she would hunt him down eventually.
- Luke, I Am Your Father: Sarah is led by the mummies to a lich-version of her father Dekalb. Initially, Sarah was scared seeing the zombified corpse until she realized it was her father who still retained some portions of his humanity. They then share a hug after not seeing each other for over a decade.
- Mercy Kill: Sarah shoots Ayaan in the head since the latter has became a lich.
- Monster Mash: Boy, this novel has a lot. In addition to The Undead and zombies, we get zombie werewolves, ghosts, phantoms, mummies, witches, wizards, and an Eldritch Abomination.
- More Dakka: Several times full automatic fire is used by both sides.
- Next Sunday A.D.: As mentioned below.
- Time Skip/ 20 Minutes into the Future: The novel takes place 12 years after the events of Monster Island where Sarah is now a 20 year-old woman. Since Monster Island and Monster Nation in set in 2005, that would make Monster Planet set in the year 2017.
- The New '10s: Thought it is not mentioned in the novel itself, it is set in 2017 as pointed out above.
- Odd Friendship: Sarah befriends a mummy named Ptolemy.
- Lich!Ayaan also befriends an zombie werewolf named Erasmus.
- Our Werewolves Are Different: Erasmus is described as an undead werewolf who became one after Leipzig, Germany was overrun with zombies. He befriends Ayaan.
- The Quisling: Human servants work for the Tsaverich in exchange from being turned into zombie chow.
- The Reveal: Mael Mag Och being the Big Bad, was playing the survivors the whole time for 12 years, even fooling Sarah that she was talking to the spirit of the U.S. Army Ranger Jack (who died in Monster Island and turned into a zombie).
- Riddle Me This: Mael Mag Och's test to Sarah was to answer the following riddle: "What is more important than the end of the world?". The answer the whole time was "The Next Day" which has been the situation of the world for roughly 12 years as remnants of humanity fought on to survive that long.
- She Who Fights Monsters: Sarah makes it clear she kills liches, even if it would mean her father or her close friends.
- Shotguns Are Just Better: The mummies that accompany Sarah use the Benelli M4 pump-action shotgun as their weapons.
- Shown Their Work: The OICW prototype weapon
Sarah finds in Governor's Island was developed around the late 1990s and shelved in 2004. Since the original outbreak occurs in 2005, it could be assumed the U.S. military were deploying almost anything that could be used to fight the zombies, including untested prototypes. - Sudden Sequel Death Syndrome: A lich!Ayaan crushes Dekalb's head with a sledgehammer, much to the horror of Sarah.
- Ayaan counts as one as well.
- The Unintelligible: Ptolemy the mummy tends to speak in nonsense riddle-like phrases, much to the annoyance of Sarah.
- Viking Funeral: As part of Due to the Dead after Sarah kills Lich!Ayaan, she burns the body though the heart remains. She then buries Ayaan's heart in an unmarked grave.
- Walking the Earth: Ayaan, Sarah, and Osman travel from North Africa to the Straits of Gibraltar then take the a trans-Atlantic route to New Jersey then to New York then fly a helicopter all the way to Colorado.
- You Killed My Father: Sarah says this word-for-word just as she is about to deliver a mercy kill to a lich!Ayaan.
- Zombie Apocalypse: Continues from Monster Island and has lasted for more than a decade.
