Steve Banning (Dick Foran) is reminiscing with his son John (John Hubbard) and his girlfriend Isobel (Elyse Knox) along with a friend of the family about his adventures in Egypt thirty years before. He and his party had come into conflict with the priest Andoheb (George Zucco) who was outraged that they wished to investigate, and effectively defile, the tomb of a long dead princess. He had sent the Mummy Kharis after them to stop their meddling, but Steve and company had overcome them - or so they think, for now, decades later, the elderly Andoheb has sent his disciple Mehemet Bey (Turhan Bey) to the small town of Mapleton to exact delayed revenge...
A mummy's tomb doesn't particularly feature in this, the sequel to The Mummy's Hand (as you can tell from extensive flashbacks), which was scripted by Griffin Jay and Henry Sucher from Neil P. Varnick's story. What does feature is Lon Chaney Jr adding to his roster of classic monsters from Universal's golden age, but this was a far more demeaning role than the one he essayed as The Wolf Man as basically he was required to shuffle around very slowly: no lines, no facial expressions, and very little dignity. Although top billed, he doesn't appear all that often, being trundled on like a shock effect at various stages of the story.
Surprisingly, this was a pretty big hit even though it looks like a standard B movie nowadays, which may explain why there were two further instalments after this one. Also unusually, once Mehemet reaches Mapleton and settles down into the disguise of a graveyard caretaker (this is where the tomb aspect comes in, I suppose) he sets about killing of the cast of the previous film, the ones who deigned to appear anyway, and they are dressed up in old age makeup. So Kharis is despatched to strangle Steve, which he does (Steve helpfully left the balcony door open), leading to possibly the highest number of sensational newspaper headlines to be seen in a film.
Although Kharis moves at about one mile an hour, and along streets at night, he manages not be be caught, much less seen - the only person who does encounter him and lives is driven into a fear-induced coma. Babe (Wallace Ford) from The Mummy's Hand shows up in town with a whole host of reporters, claiming he knows that there's a supernatural explanation behind the deaths (which include Steve's sister, played by Mary Gordon, yes, Mrs Hudson from the Sherlock Holmes films gets offed too). But no sooner than he sends the reporters on this scoop he gets throttled himself. Things are complicated by the de rigueur female element, as it wouldn't be a proper mummy movie if the monster didn't carry off a woman at some point, although this is at Mehemet's bidding and you'd have thought even a second division hearththrob like Bey would have more luck with the ladies instead of resorting to that. Overall, it's average of its type, but fills an hour-shaped hole for fans.