In medieval England, a usurped throne is the center of turmoil. The rightful heir is an infant with a distinguishing birthmark, hidden away by a band of rebels led by the Black Fox. Hubert Hawkins, formerly a carnival performer, is enlisted by the Black Fox to carry out multiple missions, including infiltrating the castle of the pretender king. Disguised as Giacomo, the king's new jester and an assassin in reality, Hawkins must navigate a web of deceit and danger, managing to charm and bumble his way through each precarious situation. He also struggles with a rapidly switching identity, trying to maintain his cover while assisting the royal baby’s rescue.

Inside the castle, Hawkins faces numerous challenges, including the king’s treacherous advisor, Lord Ravenhurst, who suspects everyone and trusts no one. Meanwhile, Princess Gwendolyn and her maid Jean complicate matters with their own interests and agendas. Surviving poison, secret passages, and deadly jousts, Hawkins has to rely on his wit and luck to protect the baby while avoiding detection. The plot twists and turns as alliances shift and Hawkins' loyalty is put to the ultimate test. Unbeknownst to Hawkins, every step he takes is riddled with potential traps that could unravel the rebels' plans and seal the fate of the true heir to the throne.