The Serpent's Shadow is a 2012 fantasy/adventure novel by Rick Riordan and the third and final book in The Kane Chronicles trilogy. Rick Riordan announced the book on January 9th, 2012 on his blog, and it was released on May 1st, 2012.
When young magicians Carter and Sadie Kane learned how to follow the path of the ancient Egyptian gods, they knew they would have to play an important role in restoring Ma'at—order—to the world. What they didn't know is how chaotic the world would become. The Chaos snake Apophis is loose and threatening to destroy the earth in three days' time. The magicians are divided. The gods are disappearing, and those that remain are weak. Walt, one of Carter and Sadie's most gifted initiates, is doomed and can already feel his life force ebbing. Zia is too busy babysitting the senile sun god, Ra, to be of much help. What are a couple of teenagers and a handful of young trainees to do?
There is, possibly, one way to stop Apophis, but it is so difficult that it might cost Carter and Sadie their lives, if it even works at all. It involves trusting the ghost of a psychotic magician not to betray them, or worse, kill them. They'd have to be crazy to try. Well, call them crazy.
With hilarious asides, memorable monsters, and an ever-changing crew of friends and foes, the excitement never lets up in The Serpent's Shadow, a thoroughly entertaining and satisfying conclusion to the Kane Chronicles trilogy. 
This book begins when Carter and Sadie Kane travel to Dallas, Texas, the 51st nome, with their initiates and meet J.D. Grissom, the leader of the nome. They tell him that they need a heavily guarded magic scroll from the King Tut exhibit at the Dallas Museum of Art, or his nome will get attacked and destroyed by the forces of Apophis, the chaos snake, who will rise, swallow the sun, and destroy the world in three days' time. Sadie sees a face in the wall, which tells that they will not understand the scroll and they instead need a golden box. However, the nome is attacked, and the scroll is destroyed. To save everyone from getting killed, Sadie summons Ma'at, repulsing the forces of chaos but almost losing her life. They discover that all of the 51st nome has been destroyed, and all of the magicians killed by the minions of Chaos. At the 21st nome in Brooklyn, they discover that the golden box Sadie was told to retrieve by the wacko magician, (Uncle Vinnie Aka setne) is the shadow box of King Tut.
Horus, the Egyptian God of War, visits Carter as a pigeon and hints a connection between shadows and statues. Carter suspects that there is a better way to execrate Apophis than perhaps blowing himself and Sadie into crazily small pieces, and decides to consult Thoth, the Egyptian god of Knowledge. He tells everybody at dinner and Sadie makes him go to their school dance. During the dance, Sadie meets Anubis, her godly boyfriend, and he suggests that the sheut is like a computer backup drive, but Shu, god of wind, and also Anubis' great-grandfather breaks them up later. Sadie gets an idea about using Bes' sheut to give him back his ren.
The Russian magician they met last year comes with bad news. Sadie takes him to the First Nome to meet Amos. He tells them that the rebels, led by Sarah Jacobi and Kwai, have teamed up with Apophis. Amos tells Zia and Sadie to visit Bes. Meanwhile, Carter and Walt go visit Thoth. Thoth is being attacked by demons. Walt and Carter repulse them, and Thoth helps them understand who Setne is. They realize they have to visit the Land of the Dead at his trial and persuade Osiris to help them.
When Zia and Sadie are visiting the House of Rest, Sadie realizes that Amos is calling on the Path of Set, god of evil, who he once hosted. Tawaret, hippo goddess, tells them where Bes once hid his sheut. Carter, Sadie, Zia, and Walt meet and exchange information. They meet Osiris, lord of the dead, and persuade him to let Setne go with them. Sadie and Walt go to look for Bes' sheut, while Zia and Carter go with Setne to find The Book of Thoth.
They go to the serapeum of Apis, and later Setne tricks them by giving orders to Bloodstained Blade to kill them. Meanwhile, Sadie and Walt visit the goddess Neith, who tells them she will help them if they can survive her hunt till sunset. They survive by using their shen amulets to split up and transfer to each other's side, and then in the end right before sunset Sadie tricks Neith by mesmerizing her with tales of hunting jelly babies and the likes. Walt uses the rest of his energy to revive Bes' sheut, and then he survives by becoming the host of Anubis.
He realizes Setne's plan and tells Sadie to go help Carter and Zia. Meanwhile, they enter the Land of the Demons, and Carter and Zia kiss. Carter realizes that Zia has become the host of Ra. They find the sheut and Setne binds them with the Seven Ribbons of Hathor. Sadie comes to help and they bind Apophis's shadow to the statue. The shadow sends a distress call to all forces of Chaos, and they arrive.
Tawaret arrives with the gods from the Fourth House (Divine Nursing Home) and saves them from a tragic death. When they return to the mortal world, the Brooklyn House is at the First Nome, helping Amos and the others protect it. Ra is reborn with Zia as his host and is not senile anymore. The other gods come to help them, while Ra gives Carter the pharaoh's throne. He orders the other gods to help. They enter the First Nome to help protect Amos against the rebels. Apophis eats Ra, and then Sadie and Carter execrate his shadow. He regurgitates Ra and dies. Ra and the rest of the gods retreat from the world.
Carter and Sadie go to see their father to report Setne's escape. Their father is just happy that they're alive and succeeded in saving the world. Sadie talks to her mother who asks her to be careful because her gift of prophecy has shown her visions of "other gods" and "rival magic".
Carter takes Zia out on a trip at the Mall of America. She tells him that she will be staying in Brooklyn House. They share a passionate friendship and start a relationship. Meanwhile, Bes and Tawaret finally get together after many centuries. Walt, now the host of Anubis, dances with Sadie and the pair also have a romantic time.
The book ends with an invitation to anyone with pharaoh's blood to join the House of Life. Sadie also mentions having to check out "unexplained magic" at Long Island.
- Carter Kane: age 15, Carter is a descendant of Ancient Egyptian magicians; he is one of the main protagonists. Described as always dressing "impeccably" in khaki pants, dress shoes, and button-up shirt. Sadie Kane thinks he has no style. The host of Horus, his main weapon is a khopesh an Ancient Egyptian sword favored by guards of the Pharaoh. His specialty is combat magic.
- Sadie Kane: age 13, Sadie is Carter's sister and shares his magical ability. She was raised in England by her grandparents after her mother died. She has light skin, caramel colored hair, which she usually dyes with streaks of bright colors, blue eyes, and never goes anywhere without combat boots. She is a powerful and natural magician who can read hieroglyphics and understand Ancient Egyptian. She becomes the host of Isis.
- Zia Rashid A powerful magician who Carter Kane has affection for. Considered the most promising student of the First Nome. Also a powerful fire elementalist. She is the unknowing host to Nephthys ( in The Red Pyramid ). Later the host to Ra.
- Walt Stone An initiate, a sau, who Sadie Kane has affection for. He suffers from the curse of Akhenaton. He is later the host of Anubis.
- Amos Kane
- Anne Grissom
- Felix Philip
- Jasmine Anderson
- JD Grissom
- Julius Kane
- Ruby Kane
- We Crash and Burn a Party
- I Have a Word with Chaos
- We Win a Box Full of Nothing
- I Consult the Pigeon of War
- A Dance with Death
- Amos Plays with Action Figures
- I Get Strangled by an Old Friend
- My Sister, The Flowerpot
- Zia Breaks Up a Lava Fight
- “Take Your Daughter to Work Day” Goes Horribly Wrong
- Don't Worry, Be Hapi
- Bulls with Freaking Laser Beams
- A Friendly Game of Hide-and-Seek (with Bonus Points for Painful Death!)
- Fun with Split Personalities
- I Become a Purple Chimpanzee
- Sadie Rides Shotgun (Worst. Idea. Ever.)
- Brooklyn House Goes to War
- Death Boy to the Rescue
- Welcome to the Fun House of Evil
- I Take a Chair
- The Gods Are Sorted; My Feelings Are Not
- The Last Waltz (for Now)
- Two characters from The Heroes of Olympus, Drew Tanaka and Lacy, demigod daughters of Aphrodite, attend the school dance. They mention that they both go to a summer camp (Camp Half-Blood). Their home is mentioned again right at the end of the book as Sadie describes 'rival magicians and gods as close as Long Island'. Which most probably refers to the Greek-Roman gods, and by magicians, the demigods at Camp Half-Blood and Camp Jupiter.
- Rick Riordan makes a few Doctor Who references in this book.
- Shu, Anubis's great grandfather, would (when she is also Isis) be Sadie's grandfather
- Ruby Kane, in the book, tells her daughter Sadie Kane that she has not lost the gift of foresight and sees a conflict with other gods and magic which is still unclear. It would most likely be Greek-Roman, since Sadie said she and Carter have to go to Long Island (Camp Half Blood's location), due to other magic. It is likely a reference to the chapters The Son of Sobek, The Staff of Serapis and The Crown of Ptolemy from the book Demigods and Magicians where Carter, Sadie, Percy, and Annabeth team up against Setne's efforts to mix Greek and Egyptian magic.
- In The Last Olympian (graphic novel), the security guard at the Empire State Building can be seen reading The Serpent's Shadow.