The illustration shows the Lord High Executioner coming down the stairs.
Sue and her younger brother, Eddie, are American tourists in London. They have spent an average day in London, eating burgers, riding in double-decker buses, and visiting old buildings. As the story opens, Sue and Eddie are touring the infamous ominous Terror Tower. Sue did not want to go, but Eddie pleaded with her. Being a good sister, she does take the opportunity to tease him about his tendency to get scared a lot, especially at movies.
Inside the castle, the guide leads the tourists around the various rooms, showing them empty jail cells and torture chambers. The guide spends a good amount of time introducing the various tools of torture, such as the rack and thumbscrews. Sue wants to take a picture, but she can't find her disposable camera. Her brother produces it from his bag and it is revealed that Eddie is a gifted pickpocket.
During the tour, Sue spies a man in black following their every move through the castle. The tour guide leads the group into a small barred cell and tells them the tragic story of Prince Edward and Princess Susannah of York, two tween royals who were sentenced to death by the King. Sue tries to listen to the story, but gets distracted by Eddie breaking her camera and misses the end of the story.
Once Sue and Eddie stop bickering about the camera, they realize that the tour has left them behind. They walk out into the steep narrow stairwell and can't hear or see anything. The mysterious man attempts to capture the children. The siblings still aren't quite sure what is going on, but the man is wearing a cape.
An extended chase down tunnels and sewers follows. Inside the sewer, a wave of rats move in on the humans. The two children think quickly and grab onto the metal rings descending from the ceiling, lifting their bodies up out of the rats.
Once the rat-tide subsides, the children lower themselves down and escape out into the parking lot. They discover that their tour bus left without them. But luckily the trusty night guard tells them in a thick Scottish burr where to call for a cab.
The cab delivers them to their hotel, where they're sure their parents, who came to London on business, are bound to be back. When the children try to use the money their parents gave them, they discover it is worthless. The cab driver agrees to wait while they run up to their room for the money. Inside their hotel room however, they discover the suite to be empty, with no record of any family having registered. Also, when questioned by the concierge, the children can't even remember their last name.
The children dine and dash in the hotel restaurant, fleeing to stiff the taxicab driver as well. Running through the kitchen corridors, the man in black blocks their path. He accosts Eddie and forces him to give up the three white stones he apparently lifted from the man in black earlier. Eddie does so and the man in black uses the stones to bring the children back in time. Yet Sue and Eddie do not realize they have gone back in time and are convinced that the medieval-looking grog shop they have wandered into is an elaborate costume party. Running out of the abbey, Sue loses Eddie and realizes they aren't in the twentieth century anymore.
Sue pays a peasant for a hiding space with the funny money and is shocked to discover that it is actually real gold coins. When the man in black strolls around to the peasant’s hut, the peasant wastes no time turning Sue in. The man in black commands some soldiers to lift the basket into his cart. The peasant apologizes to the basket for turning the girl in, but she just could not go against the man in black, he is the Lord High Executioner. Refusing to defer to the Lord High Executioner, Sue is escorted back to the castle, where Sue is reunited with Eddie. The two are locked tight in a cell, but not before the pale man in black taunts them with the white stones. Once the dignified and potent officer, whose functions are particularly vital leaves, a sorcerer appears.
The white-bearded sorcerer introduces himself as Morgred, the king's personal magician. He reveals that Sue and Eddie are actually Princess Susanna and Prince Edward. Mordred sent them to the future with new memories in order to survive in a new, distant time. But alas, their memories were not complete. Their parents are dead and their uncle, the King, has imprisoned them to await their death. Morgred used the magic stone balls to send the two children as far into the future as possible and gave them false memories.
The children try to make a break for it out the open cell door, but Morgred bewitches the children and they freeze in place. He apologizes with tears in his eyes, but if he lets the children escape, the king will kill him. As Morgred keeps wailing, Eddie reveals to Sue that he has swiped the stones yet again. Remembering the ancient Latin words Mordred used to cast the spell, the two cast themselves back into the present.
Back on the tour, they finally hear the rest of their story: On the night of the execution, the children mysteriously disappeared. A bearded man joins the children and thanks them for bringing him with them. Morgred asks for the children to call him Mr. Morgan since he will be his new father and offers to cast a food spell to cure their hunger. The book ends, as Sue wittily replies that they had enough spells for a lifetime and asks them if they would want any burgers instead.
- The premise of two heirs to the English throne mysteriously vanishing is actually based on true events. In 1483, Richard III placed his two nephews, Edward V and Richard, Duke of York, in the Tower of London (then a palace) and were never seen again. It is not known what happened to the two young princes, but most rumors say they were killed.
- There was a gamebook sequel called Return to Terror Tower in the Give Yourself Goosebumps series.
- This was the first Goosebumps book to feature orphaned children, and feature no monsters or supernatural beings.
- The UK version featured someone trapped in a dungeon.
The Lord High Executioner appears as a background monster in the 2015 Goosebumps film, and has a similar appearance to his book appearance.