After his Benaras sojourn, Byomkesh Bakshi is back in action with a new riveting case. Santagola has become a hub of illegal weapons trade and Bengal Government requests sleuth Byomkesh Bakshi to investigate the case. On arrival, Byomkesh, his wife Satyabati and his friend Ajit are welcomed at the state guest house. As soon as Byomkesh Bakshi starts his investigation, he zeroes in on few well-known people of this city, who could be possible suspects. However, he realizes that these men are way too powerful and he will never be able to search their warehouses and mills. In the meantime, a demented man named Amrito claims that he has seen a demonic horse-riding figure roaming around the jungle. Amrito is sent to the jungle to observe this phenomenon. Next morning, his bullet ridden dead body is found inside the jungle. As Byomkesh delves deep into the case, a lot of well-respected men will be unmasked as he uncovers the dark mystery of Santagola.