On holiday in Egypt with George and Emily Hacker (Christopher Connelly and Martha Taylor), her archaeologist father and journalist mother, 10-year-old Susie Hacker (Brigitta Boccoli) is approached by a mysterious blind woman, who gives her an amulet with a blue-jewled eye in the center. Soon after, George is struck blind by a bright piercing blue light when he enters a previously unexplored tomb. But his assistant is not so lucky as he falls from a false floor bottom to his death on spikes in a boody-trapped chamber.
Upon arrival back in New York, George is informed that the loss of his eyesight will only be temporary. Susie begins to act strangely, and her younger brother Tommy (Giovanni Frezza), who stayed behind in New York with the family's au-pair Jamie Lee (Cinzia De Ponti), is also affected by the mysterious amulet. Emily soon discovers that both of her children are appearing and disappearing out of their rooms every day and night. Both Susie and Tommy have gained supernatural access to dimensional doorways. A few days later, George's eyesight returns, and he describes the design on the wall of the tomb he'd entered to a colleague called Wiler, Wiler guesses that it may be the Sacred Symbol of the Grand Shadow, a sight of terrible evil.
Over the next few days, the Hacker family experiences more odd happenings. A scorpion appears in a desk drawer when George opens it. Later, Jamie Lee is menaced by a snake that attacks her in the apartment building cellar during a game of hide-and-seek with the kids. Then, Emily discovers piles of sand on the floors of their bedroom and adjacent rooms. Also, the building superintendent dies in a supernatural freak accident then the elevator he's riding in malfunctions, and drops open the floor of the elevator car, making him plunge to his death. A little while later, Luke Anderson (Carlo De Mejo), an eccentric colleague of Emily's, arrives at the apartment to work with her about her latest journalist work detailing her travels in Egypt. When Luke hears a noise coming from Susie's bedroom, he enters it and tries to force open a jammed bedroom door. He opens it only to be sucked into the dimensional portal and finds himself transported to the deserts of Egypt where he later dies from dehydration in the vast, arid desert. The Hackers think Luke's disappearance is merely one of his practical jokes, but they never learn of his fate, nor find any trace of him.
Jamie Lee takes the kids out to nearby Central Park to play where she takes photos of them. A woman picks up a discarded Polaroid photo taken of Susie. It shows nothing but the amulet against the grassy background. The woman contacts a man called Adrian Marcato (Laurence Welles) with her find. The next day, the woman drops the Polaroid down to Mrs. Hacker from a window overlooking the pavement. Marcato's name and phone number are written on it.
Meanwhile, Susie and Tommy continues to appear and disappear from their bedrooms on what Tommy called "voyages." Soon, Jamie Lee herself disappears after entering Tommy's room. When Emily asks Tommy if he seen Jamie Lee recently, he tells his mother that Jamie Lee has not come back from her own voyage. That evening, George's colleague Wiler is killed when he gets bitten by a cobra that magically appears in his office as he is looking over the photo of the amulet that Hackers have given him. The photo magically disappears and reappears in Susie's hand as she recovers from a mysterious fit.
George and Emily track down Marcato to his antique shop and demand to know what his involvement is. He tells them about the evil symbolism of the jewel, and suggest that Susie has absorbed its energy. He also tells the skeptical couple to at least make sure she doesnt have the amulet in her possession. When George and Emily find the amulet in Susie's bedroom drawer, she appears to them glowing with an unearthly blue light, and then faints. Marcato is called to the Hackers apartment to examine Susie, but is possessed by her inner voice crying for help, and falls to the ground, bleeding and foaming at the mouth. Marcato regains consciousness and succeeds in linking minds briefly with George, showing him a glimpse into the eldritch Egypt his children have been visiting. Susie is then taken to a nearby hospital where the physician Dr. Foster (Lucio Fulci) examines her and is baffled by her mysterious illness. An X-ray taken shows the dark shape of a hooded cobra mark in her chest.
While, Emily maintains a bedside vigil for the near-comatose Susie, Tommy is alone at the apartment when he is partly affected too. Suddenly, Jamie Lee turns up, bursting through a wall as a briefly reanimated rotting cadaver before she drops dead. A strange blue light of negative energy is shown flowing from Tommy, the bed-ridden Susie, and the dimensional doorways and channeled into Marcato's home where he is inciting a spell in the ancient Egyptian language. George goes to see Marcato again, who tells them that he can stop worrying about his children. Through an ancient Egyptian spell, Marcato has channeled all the evil energy away from George's children and the curse is now on him. Marcato gives George the amulet and tells him to discard it so the curse will not affect anyone else. That night, Marcato is killed at his shop when the re-animated carcasses of his stuffed birds come to life and tear him to pieces. At the hospital, Susie wakes up to see her grateful mother by her side and both are happy that Susie all better. The following morning, George, following Marcato's last suggestion, flings the amulet into the East River, bringing an end to their ordeal.
In the final scene back in Egypt, the mystical blind woman once again appears and gives the exact same amulet to another young girl, intending to continue the curse for the forces of darkness, bringing it full circle.