The Day of the Djinn Warriors is the fourth novel and deals with more of the Sachertorte family's past, as well as the encounter with the newly changed Layla Gaunt. Dealing with thefts, hauntings and a red-hot mystery, it is a race against time for John and Philippa Gaunt to outwit the wicked Iblis. But can the djinn twins stop Iblis now he has awoken the ancient warriors of a long-dead emperor from their sleep? John and Philippa attempt to rescue their mother from her fate as the Blue Djinn of Babylon (a djinn that is beyond good and evil, who has powers over all.) There is only one way to ensure that their mother doesn't succumb to this fate, and that is to find the true successor to the last Blue Djinn of Babylon, the sister of their friend, Dybbuk Sachertorte, Faustina. They discover that an aging curse has been placed on their father and if the twins are gone too long, he will rapidly become an old man. As the twins and their friends travel around the globe on their rescue mission, they notice that something very strange is happening: An evil force has awakened the terracotta warriors created by an ancient Chinese emperor, and someone with very bad intentions has cast a spell possessing the soldiers with wicked spirits. And now, the very fate of the world hangs in the balance.
During this time, museums all over the world are reporting robberies of valuable jade artifacts from their collections, as well as bizarre hauntings.
Faustina has been missing for a long time, having lost her body after she possessed the body of the English Prime Minister. Now her body and soul are separated, and the twins, along with their friend Mr. Rakshasas and his butler, Groanin, must retrieve Faustina Sachertorte's body and her spirit as well, each of which has been separated, one apparently remaining in London, where it was stored in with the Wax Dummies at Madame Tussaud's. But her soul has gone to a small island on the Hudson River in Upstate New York. To retrieve it, John and Mr. Rakshasas will have to leave their own bodies behind as well, and travel through a gate in the Egyptian temple in the Museum of Natural History in New York City.
John bequeaths his Djinn Power to Phillippa and goes with his friend to the museum, while Phillippa and Groanin set off to England. When they get there, however, they find that Faustina's body is gone, apparently stolen from the Wax Museum along with two other dummies. They track the thief to Italy, where the woman who stole the dummies has used Faustina's body to replace the supposedly "incorruptable" body of a young saint.
While on their mission to retrieve Faustina's soul, however, John and Mr. Rakshasas discover that a clay statue of a Chinese Warrior seems to have been absorbing all the spirits that normally inhabit the museum. What the warrior is doing with the spirits isn't known, although apparently once the spirit is absorbed, it cannot return. And without their bodies, John and Mr. Rakshasas are also at risk of falling to the creature. Even the Guardian of the temple, immune as he is to being absorbed, feels pity for the souls absorbed by the clay creature. Humans cannot sense that the restless souls are now gone, but the way the creature stalks the halls of the museum has led the workers to label it as haunted or cursed.
Faustina seems to have run into a strange encounter when she was bodiless. Her spirit was somehow sucked into a strange vortex and she wound up in a strange land, where a man in a jade suit had summoned all the spirits and the clay warriors were absorbing them. She only narrowly escaped being absorbed herself, and had to slowly make her way back to the island.
Dybbuk persuades his mother to take him to Las Vegas, where he gets to see his favorite act, a magician named Adam Appollonius. In reality, he wants to meet his real father, a rotter of a Djinn who is a member of the Ifrit Tribe, a Tribe of really nasty Djinnis. While he is there, he amazes Adam Apollonious with a series of "magic tricks" that make use of his Djinn magic, and the magician offers to take him on as a magic prodigy. Dybbuk readily abandons his mother and the Djinn for a career as a stage magician. Little does he know that his father's spirit is possessing Adam Apollonious and that he is using Dybbuk to be a fall guy for some major crime he is planning. Nor does Dybbuk know that by using his Djinn magic in this fashion it will eventually be taken from him.
He rides high on his fame and money, until his father persuades him to do a trick that will rob him of his spirit, and to include millions of children around the world of theirs, also. But what could Iblis, Dybbuk's father, want with all those souls? What sort of terrible crime could he be planning? And can he be stopped by two Djinn children, even a set of the ultra-lucky twins?