The Gone Dead Train

When Al winds up with a third inexplicable death, he asks Catherine to investigate further despite the lack of a cause of death. When the mother of one of the victims also inexplicably dies, the cause points to an obscure, usually non-fatal disease, and a tattoo parlor run by a former coroner from Reno, Nevada. Meanwhile, Riley and Greg investigate the death of a woman who appears to have been raped, and her body dragged far from the scene.