Taking place several years after the events of "The Mummy's Tomb", in this third film in the series about Kharis the Mummy, we find Kharis somehow (once again) managed to prevent being destroyed at the end of the last film. As the unfortunate professor at the local university discovers, when he starts brewing up some Egyptian Tana leaves to see if they really can make you immortal, only to have Kharis (Lon Chaney Jr again) burst in and kill him, so he can steal the potion for himself.
Its never explained where Kharis appeared from, or where he's been hiding all these years, but anyway. Whilst this is going on, Egyptian Priest Yousef Bey (played by a young-ish John Carradine) has headed over to America to retrieve Kharis, and the Mummy of the Princess Ananka, who's currently on display in some museum in Massachusetts. But having broken into the museum, they discover that Ananka's body has disappeared.
Meanwhile, across town, one of the local girls, Amina (Ramsey Ames), who happens to be of Egyptian descent, is getting strange flashbacks about Egypt (you can see where this is leading). Yes, it seems Ananka has taken over the soul of one of her descendants, who happens to be conveniently living nearby and now Bey and Kharis are looking at taking her back.
Having kidnapped Amina, and with several townsfolk having fallen victim to Kharis, the Sheriff and the local vigilante mobs are out in force. Setting things up for a final showdown, which could spell the end, not only for Bey and Kharis, but also the kidnapped Amina (or maybe not, but if you want to know what happens, you'll just have to see this one for yourself).
As with the previous films, if you liked them you should like this. Was kind of surprised to see George Zucco back in this as the Egyptian high priest, seeing as he appeared to die during the intro of the previous film. Plus there was no explanation of what happened to Kharis the Mummy between films. But these points aside, this still proves to be an adequately entertaining B&W horror sequel.