A valuable gem, "The Eternal Light," is stolen from a renowned Egyptian tomb and falls into the possession of Professor Morlant (played by Boris Karloff). Believing in the powers of ancient Egyptian gods, Morlant is convinced that the gem will grant him immortality. On his deathbed, the professor instructs his servant, Laing (played by Ernest Thesiger), to bind the gem to his hand after he dies. He also warns Laing that if the gem is stolen, he will rise from the dead to seek revenge.
After Morlant's body is sealed in the tomb behind his house, Laing steals the gem. The professor's heirs, Betty Harlow (played by Dorothy Hyson) and Ralph Morlant (played by Anthony Bushell), arrive at the ancient house to settle the estate. Obsessed with greed, Morlant's lawyer searches the house for the gem, joined by a fraudulent parson (played by Ralph Richardson) and Aga Ben Dragore (played by Harold Huth), both of whom also desire the gem for themselves. After the deceased Morlant discovers his gem is stolen, he rises from his tomb to retrieve it. The professor strangles his servant and regains his gem. He returns to his tomb and dies. The police arrest the lawyer, parson and Dragore after they attempt to steal the gem. "The Eternal Light" is returned to the heirs, who use it to start a new life.