One quiet evening, Septimus Culthorpe stumbles into 221B Baker Street. He introduces himself as the leader of the Secret Seven - a mysterious group of seven monks who lead a simple lifestyle and reside in Grimstone Priory, an old cottage in Sussex.
Two of the seven monks have been murdered in unusual circumstances. The weapon remains unknown and Culthorpe suspects that both suffered a heart attack.
However, he is apprehensive of the letter that both men received the day prior to their death.
Alarmed by the two horrid and unusual murders in Grimstone Priory, Culthorpe seeks the assistance of the detective and his partner.
The group prepares a plan - Holmes and Watson will temporarily substitute the deceased monks and observe the possible suspects in order to uncover the mystery.
Once settled into the simple village life, Holmes and Watson gradually reveal the secrets that lie in Grimstone Priory.
The days following their arrival result in a series of strange events including the mystery of some missing jewels, doubtful identities of the monks, and brutally slaughtered animals.
Can Holmes and Watson solve the case before a third member of the Secret Seven is killed?