The Apothecary Melchior series plunges the reader into 15th century Tallinn when Estonia stands at the edge of Christendom, the Church's last foothold before the East: a town of foreign merchants and engineers, dominated by the mighty castle of Toompea and the construction of St Olaf's Church, soon to become the tallest building in the world... Apothecary Melchior is a divisive figure in the city: respected for his arcane knowledge and scientific curiosity but also feared for his aura of mystical power. When a mysterious murder occurs in the castle, Melchior is called in to help find the killer and reveals a talent for solving crime.

But a serial killer is loose in Tallinn, and Melchior is tested to the limit in a plot with as many twists and turns as the corridors of the castle itself. Melchior uncovers a mystery surrounding St Olaf's church and a secret society that has been controlling the town for years, revealing truths that may spell danger for any who dare to speak them aloud...