While investigating one of Sherlock's cold cases, Joan discovers an out-of-place rock in the garden of a murder victim. Joan enlists a geologist to study the rock and they learn it houses a complete dinosaur fossil. The rock is later stolen from the police evidence room. Tracking down a known smuggler, Sherlock and Joan discover the smuggler murdered and the fossil destroyed. They eventually expose the curator of a natural history museum committed the murders to hide the proof of a scientific theory that would have cost him and his mentor their legacies. Meanwhile, Sherlock has his hands full as a sponsor when Randy's addict girlfriend turns back up in his life.