A missionary woman has disappeared in Spitalfields, one of London's most dangerous districts. When Sherlock Holmes in called on to find her, he discovers enormous, highly intelligent rats have made their home under the streets of London. Holmes is forced to confront the horrors of his past and science gone mad. Word of this phenomenon draws the attention of rising zoologist G.E. Challenger, who decides he must meet the creatures' creator, one Dr. Moreau. As in the author's ‘Never Meant to Be’, the worlds of Sherlock Holmes and H.G. Wells once again come together, this time to uncover the truth behind the Giant Rat of Sumatra.