When a serial bomber becomes active again after being dormant for six years, Watson seeks help from Shinwell Johnson, a former patient whose life she saved when she was a surgeon. Also, Holmes senses Watson is unhappy and questions whether she is still fulfilled by her detective career.

Sherlock and his father, Morland Holmes, attempt to repair their strained relationship upon learning of a death within their family. Also, Holmes and Watson discover a link between their latest case and the world of Egyptian antiquities when they search for a killer who tried to mummify his victim.