The movie opens with titles and credits over a pen and ink drawing of four zombies walking through the mist. There is a panning shot of the shoreline, then a car approaching on a dirt road at dusk. The driver, Sam (Gene Roth) is transporting Jan Peters (Autumn Russell) to her grandmother's house near Dakar on the African continent. It is a bumpy ride and Jan tells us it has been ten years since her last visit. On the highway a man blocks the road. Sam runs the man over and continues to drive like nothing happened. Jan is horrified and demands Sam stop the car. Sam explains, "It wasn't a man, it was one of them." They arrive and one of the headlights on the car shows sign of the collision. Waiting outside the house is Jan's grandmother (Marjorie Eaton). Mrs. Peters tells Jan, "There's no one on the road." Despite her protests, Sam and Mrs. Peters go on like nothing happened. They hear the horn of a ship offshore.Inside the main cabin of the salvage ship we meet: Dr. Jonathan Eggert (Morris Ankrum), their diver, Jeff Clark (Gregg Palmer), the financial backer of the salvage, George Harrison (Joel Ashley) and his wife, Mona Harrison (Allison Hayes). They talk about the salvage and what each will do with their share of, "a million bucks in diamonds." Mona is a gold digger and a flirt. She shows way too much interest in Jeff. While Jeff might like to reciprocate, fooling around with the wife of the boss is bad for business, and his health. The ship's captain tells Harrison the launch is ready to take them to shore. They go out on deck. A man in a striped shirt swims toward the boat. When a deck hand, Johnson (Mel Curtis) leans over he is grabbed by the swimmer and pulled overboard. Harrison shoots at the swimmer. When they recover Johnson's body they discover his neck was broken. Mrs. Peters' dog barks at something approaching their dock. Mrs. Peters sees it but pays it no attention. Jan confronts her. Mrs. Peters tells her granddaughter, "You wouldn't believe me, Jan." She tells Jan the renewed activity of salvage has brought "them" back. The launch lands and Mrs. Peters and Jan greet them. She tells them she was expecting them, and adds, "I wrote. I warned you of the danger." Mrs. Peters takes them on a tour of the graveyard. She shows them every salvage party grave, the date and their nationalities: 1906--British, 1914--German, 1923--British, 1928--Portuguese, and 1938--American. She tells them theirs is the sixth attempt and there are already graves dug for them. Mona manages to fall into an open grave, panics and becomes hysterical. Mrs. Peters puts them up for the night.Harrison and Jeff plan their salvage dive scheduled for the next day. Dr. Eggert talks to Mrs. Peters. He tells her he's spent twenty years researching the legend of the Susan B. He came for the story and to complete his book. Mrs. Peters shows Eggert a picture of Jeremy Peters, captain of the Susan B. and tells him she's seen him. She recounts the legend and how the diamonds were stolen from a temple, a fight, the ship scuttled in the bay, and the crew killed. The ten men including her husband, Captain Peters, are still guarding the diamonds. She tells Eggert she returned after his death, built the house, and intends to help her zombie husband, "return to dust, to find his eternal rest."In the bedroom, Mona and Jan are screaming at the approach of a zombie. Responding to the commotion, Jeff enters with Harrison and attempts to break the zombie's back. Failing in that, he hits it repeatedly in the face with no effect at all. His attempt to choke the zombie gets him thrown across the room. Mrs. Peters waves a torch at it and it departs. "Fire, that's the only way to fight them," she explains. She tells Jan that she will help the salvage group because, "only when the diamonds are destroyed will your grandfather be able to rest." Jan is dubious of her grandmother's plan having any chance of success, but she does tell Jeff he should abandon his plan to recover the diamonds. She tells Jeff about the drive to the house and the man they hit on the road. She asks Jeff to help her find out if the man is dead. They drive down the road and stop when Jan notices something. They find the remains of the broken headlight and some seaweed. They walk up the road looking for more clues. They decide to return the next morning and follow the footprints. While Jeff goes to the car for something, a zombie picks up Jan and carries her away. Jeff follows, the zombie doubles back, still carrying Jan and attacks Jeff. Jeff drives a knife into its neck, which has no effect. It carries Jan away, past the graveyard to a mausoleum. It places her on a bench, her screams waking the remaining zombies from their torpor. They get up out of their stone sarcophagi and approach Jan. Jeff shoots off a couple of flares to hold them back. Leading the pack outside is Captain Peters (Frank Hagney). The flares keep them at bay.At breakfast the next morning Jeff explains his and Jan's adventure with the zombies. Mona thinks Jeff was set up by Jan and the zombie ambush. Mrs. Peters joins Jeff, Harrison, Dr. Eggert and Mona at the breakfast table. She thanks Jeff for Jan's rescue. Jeff and Harrison renegotiate their partnership--it is now 50/50. They return to the boat and Jeff makes his first dive. He spots the ship wreck, but complains the helmet leaks. He walks along the bottom and up to the sunken ship. A zombie appears and walks towards the ship. Jeff enters the hold of the ship, but the zombie is right behind him. He spots the safe. The zombie attacks and dislodges his air and communication lines, but not before Jeff requests to be hoisted back aboard. Jeff is brought on board, barely alive. They take him back to Mrs. Peters' house where she and Jan nurse him back to health. Mona objects when Mrs. Peters tries to administer a stimulant to help him breathe. In fact everyone except her granddaughter suspects she is trying to poison Jeff. Jan drinks some. Jan gives Jeff some of the potion. While waiting for Jeff to recover, Harrison, Mona and Dr. Eggert play cards. Mona goes in to see Jeff. She and Jan argue until Harrison comes in and removes his wife, giving her a good slap. Angry and humiliated, Mona runs from the house. When Mona doesn't return by nightfall, Mrs. Peters is convinced the zombies have her.They take the car to the mausoleum. Jeff, Harrison, Eggert and two crewmembers, Art (Lewis Webb) and Johnny (Leonard P. Geer) walk through the jungle to the graveyard. Harrison finds Mona's bracelet. Jeff, Harrison and Eggert walk on to the mausoleum. Art and Johnny are told to stay at the graveyard. The men enter the mausoleum and find Mona on the floor. The zombies get up and approach the three. Harrison goes to retrieve his wife's body. Mona wakes and sits up. They all walk out and set a fire by the door to hold the zombies back. They drive back to the house. Jan notices Mona is cold to the touch. Harrison notes that she hasn't said a word. Mrs. Peters finally announces the obvious, "She's dead. Your wife is dead Mr. Harrison." Harrison insists they stay the night in the house. That night Mona gets up out of bed, grabs a knife and walks to the room next door. She stabs and kills Art who is sleeping. Johnny wakes in time to jump out of bed and call for help. Harrison and Jeff enter the room and disarm her. With candles they direct Mona back to her room and hold her there with more candles placed in a circle around the bed. Jeff concludes, "If fire'll work here, it'll work underwater, too."The next morning, Jeff and Harrison build a fire in front of the mausoleum. They think they will be able to work undisturbed if the zombies are bottled up. They return to the boat and prepare for their dive with acetylene torches. Jeff dives first, followed by Harrison. The plan is for Jeff to torch open the safe by cutting the hinges while Harrison uses his torch to hold off the zombies if any show up. Captain Peters and half a dozen zombies approach the men working on the sunken ship. There must have been another exit from the mausoleum. Jeff completes the work on the hinges and removes the cask of diamonds. The zombies are all over Harrison and he calls topside to be pulled up. Jeff holds off two zombies with his torch. Harrison makes it to the surface and is brought aboard the ship. Jeff makes it up with the diamonds and hands the cask to Eggert. The zombies are boarding the ship. They try to repel the attack with stick torches and kerosene, but end up barricaded in a cabin. Jeff makes a makeshift torch out of a pillow case and lighter fluid. He exits the ship with the diamonds. The zombies follow anyone with the diamonds. Jeff gets back to the house. Jeff and Jan stop in to see Mona. She's attracted to the diamonds but held in her bed by the candles. Jeff and Jan go to the living room and meet with Mrs. Peters. They open the box of diamonds. Harrison and Eggert arrive in the dinghy. They make straight for the house as the zombies swim ashore and also head for the house. Harrison confronts Mrs. Peters, Jan, and Jeff and demands the chest of diamonds at gun point. Harrison takes the chest and exits. What he doesn't know is that Jeff has them in a silk scarf. Harrison goes to get his wife using the chest to lure her outside and to follow him. Mona grabs the chest and hits her husband over the head with it, killing him. She takes the chest and she and the zombies return to the mausoleum. Jeff has the diamonds and wants Jan to leave with him. Mrs. Peters tells him if he scatters the diamonds where no man can recover them the zombies will stop. They leave the house and board the launch. The zombies, Mona and Captain Peters return when they discover the chest is empty. Jeff hands the diamonds over to Mrs. Peters. She sobs as she throws them into the sea. She tells her zombie husband, "At last, Jeremy Peters, at long last." Captain Peters disappears and his empty uniform falls to the ground. We close with Jeff and Jan kissing.