Recovering from a broken leg after his ignominious fall from the Titanic, Lestrade should have had a peaceful time convalescing. But an attempt on the life of his future father-in-law makes him realise that a policeman is never really off duty. What is particularly puzzling is the arrival of a letter which simply reads, "Four for the Gospel Makers", and it isn’t the first Lestrade has been sent.

So begins one of Sholto Lestrade’s most mystifying cases, encompassing both the present and the past. He walks down memory lane, looking back on episodes in his career which never came to satisfactory conclusions and hold other clues as to who the sender of the letters is. Because whoever it is is a cold-blooded killer.