An Enigma of Revenge

Six people are murdered by a killer in Pokhara, Nepal.The killer had left clues in the form of coded letters with each murder. The investigating officer, inspector Bachha Yadav and SI Bishnu Thapa have no clue regarding the killer.
Is the killing random selection of victims or a revenge of some past incident?
Who is the killer? Is he some psychopath or a professional killer? What are his motives? If it’s revenge, what’s the reason? This leaves the police officers in a dilemma.
Inspector Yadav takes help from his childhood friend Dr Dev Prakash Khattri (DPK), a child-specialist by profession to solve the mystery and nab the killer.
After knowing the identity of the killer, Yadav is shocked. But, why? This is the main mystery of the novel.