A madman is terrorizing villagers by setting fire to churches and poisoning wells. But instead of dealing with him, Robin rescues the man and takes him to the forest. The man is a veteran of King Richard's war in the Holy Land and is suffering what we now know as Post Traumatic Stress Disorder, called Crusader's Sickness by Robin and his men. He has strange, unusual Saracen symbols tattoed on his chest.
Meanwhile Sheriff Vasey has a guest, a Middle Eastern prince who is here to broker peace, and awaiting Prince John at Nottingham Castle. He is Prince Malik, Saladin's nephew. In the forest, Will has found the prince's wagon stuck in the mud. As they examine it, they find directions to the castle and also a strange mask, which they think is used to perform dark magic. Everyone, except Robin and Djaq, comes to believe that a sorcerer is staying at the castle.
Robin has trusted Much to look after the madman, and he names him Harold. Harold seems fine when he and Much are cooking food, but when he sees the Saracen mask, he attacks Djaq with a knife and is close to slicing her throat. After that they keep him locked up in a cage. Much seems disapproving of this, but "Harold" tells him it is better.
When Prince Malik comes to recover his wagon, Robin kidnaps him. Djaq explains who he is and demands that they let him go. After the Prince tells the gang why he is in England and what the mysterious mask does, which is healing a broken mind througj acupuncture, they let him go. As he returns to the castle, the Sheriff lets it be known to Gisborne that he is actually holding Prince Malik as a hostage, and has demanded a ransom from Saladin. Quite by chance, Marian overhears this and passes the information on to Robin.
The ransom is carried through the forest by four exotic Saracen women and their male leader. Robin is about to take it, but is stopped by Djaq, who explains that the women are Saladin's finest assassins: the group are dubious about her claim, but take it more seriously when they see the lethal skills of the warrior women. The group originally assume the warriors have come to rescue Malik, but Djaq dismisses this: they then realise the prince has acted without his uncle's consent and Saladin has dispatched the assassins to kill him. Harold tells the gang that it was these women who tattooed their marks on him and drove him mad.
Robin and his men go to the castle to rescue Prince Malik. The assassins, meanwhile, having set off a diversion and killed most of the Sheriff's guards (the Sheriff is rescued by Robin and the gang, while Gisborne survives by playing dead) are about to kill Prince Malik when Robin, his men and the Sheriff engage in battle with the assassins: however, the lethal skills of the warrior women prove too much for the outlaws, and Robin and the gang are on the brink of defeat. Suddenly with a howling war cry similar to the assassins, Harold comes charging to their rescue and displaying fighting styles similar to the assassins, fights and cuts the warrior women down. Once the assassins are slain, the Sheriff orders Prince Malik to get out of Nottingham, and reminds Robin that it's "business as usual tomorrow, Locksley!". Back in the forest Malik heals Harold with the mask and they leave together to travel back to the Holy Land, Malik promising to carry Robin's tale along with his message of peace to the Saracens. Robin also compliments Much on how his good and patient nature were also of benefit to Harold.