Filmed straight after "The Mummy's Ghost", this fourth and final film about Kharis the Mummy is set several years after the events of the last film (which sort of makes you wonder what year this is supposed to be), in which the swamp that Kharis disappeared in, is being drained.
A group of archaeologists from the nearby university arrive to search the swamp remnants for the bodies of Kharis and the girl who disappeared with him, the resurrected Princess Ananka (wasn't she called Amina in that?). But soon after arriving, they find a murdered construction worker and evidence that something was dug up nearby. The engineering firm doing the drainage work are already having problems hiring locals to work in the swamp, owing to the old stories about the Mummy and his Princess stalking them at night. But this latest discovery only adds more fuel to their fears.
Needless to say, they don't find the Mummy because some nefarious Egyptian types have already swiped his body and hidden him in the remains of an old monastery nearby. Hoping to finally return him and the resurrected Princess back to Egypt, just as soon as they can find her.
Soon after, the group discovers a young woman (Virginia Christine) wandering around the swamp suffering from amnesia. Though they don't realise it, she happens to be the resurrected (or should I say re-resurrected) Ananka, and Kharis (Lon Chaney Jr again) is determined to get his Princess back, killing anyone who gets in his way (which he does quite frequently).
A fairly satisfying conclusion to the Kharis the Mummy series, though the plot is fraught with anachronisms and geographical errors. If the second film was set 30 years after the original and each sequel several years on from the last, shouldn't we be into the early 1980s at least by now? Yet it's still the 1940s. Plus, the other sequels were set in Massachusetts, yet this one appears to take place in Louisiana, so how did Kharis and Ananka suddenly turn up here? Did the people of Massachusetts decide to relocate the swamp and all it's contents to another state between films??? Also, why is there no mention of the fact that Ananka actually possessed the body of a young girl called Amina in the last film?
But you can gloss over most of these errors, as the films location and the intervening years between the sequels isn't expressly mentioned, so if you just watch it and try not to examine things too closely, the film is entertaining enough. As long as you enjoy these old B&W horrors of course.