In this book, Indy and Herman have been sent to the Charenton Academy boarding school in England. This is a fictitious school.

Page 10 reveals that two of the books written by Indy's father are The Quest of Gawain and Search for the Holy Grail. Gawain is the nephew of King Arthur in the mythology of King Arthur and the Knights of the Round Table and was involved, along with his fellow knights, in the search for the Grail.

Cerdic tells Indy he read about a tower that was entered by means of a spike stairway in a book called Men of Iron, which Indy is also familiar with. This is an actual 1891 juvenile novel by Howard Pyle.

Page 11 states that Indy has been at Charenton Academy for two months now, so he was sent there in September of 1913, probably immediately after the events of The Bermuda Triangle, where he had gotten himself into quite a bit of trouble with his father in that month, which may have prompted his "exile" to the boarding school (although Indy's father is said to be teaching a class at Oxford at this time on page 12).

Page 12 reveals that Herman's father is an archaeologist.

On page 14, Indy and Cerdic's train takes them through the county of Somerset, where many battles between the Celts and Anglo-Saxons took place in the 5th-7th Centuries, passing by the historic hill-fort called Cadbury Castle. This is all part of real world history.

On page 15, Cerdic tells Indy of the legend that King Arthur's knights are seen to ride off from Cadbury every seven years as ghosts on Halloween/Samhaim. This is a real world legend in the area.

On page 16, Cerdic says that some people believe that King Arthur was a Roman named Artorius. This refers to Lucius Artorius Castus, a Roman military commander of the 2nd Century who served in Britain.

Indy and Cerdic change trains in Bristol.

After leaving Bristol, the train pauses at a station in Llantrisant. Llantrisant is a small town in Wales, about 50 miles west of Bristol.

The train heads through the Vales of Rhondda and on to Trewen, where Cerdic's family colliery lies. "Vale" is a British term for a wide river valley and Rhondda is a former coal mining area of south Wales. Possibly, Trewen refers to the small hamlet by that name in the area of the market town Ross-on-Wye in Wales.

The Sandyford Colliery and Sydney Colliery appearing in this novel are fictitious as far as I can tell.

Cerdic's quick summation of the battles of the Britons against the Anglo-Saxons on page 39 is basically correct.

As far as I can find, the Arthur's Throne and Arthur's Fountain landmarks visited by Indy and Cerdic near Trewen are fictitious.

After finding an old ring with a dragon design, Cerdic remarks that a dragon is an old symbol of Wales. This is true.

After Mr. Sandyford's injury in the tunnel collapse, Dr. Padarn suggests putting him in the hospital in Cardiff.

Indy meets a female ghost from Arthurian times named Morgen. This is likely meant to be the legendary Morgan le Fay, a magician said to be an enemy of King Arthur in the legends, but Morgen implies she is an ally here.

Morgen tells Indy that Camlann has fallen. The Battle of Camlann is the legendary battle that supposedly saw the deaths of King Arthur and Mordred. Mordred is often depicted as an enemy of Arthur, though some accounts suggest he was an ally and possibly the king's son or nephew.

Morgen tells Indy that the allies of Arthur who have survived the battle of Camlann will have to escape with Gwenhwyfar. As Indy surmises, this was the Welsh name of Guinevere, Arthur's queen.

On page 101, Indy hears the ghostly riders giving orders and other shouts in Welsh English and something like German. Arthur's soldiers would have been Welsh (like he) and their Anglo-Saxon enemies were Germanic in origin.

On page 118, Indy refuses a fair share of the treasure from Cerdic's family, accepting only a single gold Roman denarius coin. Historically, a denarius is generally considered to be a silver coin. Roman gold coins are normally called dinars or, sometimes, novus denarius.

On page 119, Indy tells Cerdic of a passage his father had once found in an old book of Arthurian stories from France that mentioned King Arthur followed by a Prince Cerdic. Indy surmises that Prince Cerdic may have been the son of Arthur and that Indy's new friend Cerdic Sandyford may be a descendant. As far as I can find, there are no legends of a son of Arthur named Cerdic, though there is legend of an Anglo-Saxon Prince Cerdic, who would have been an enemy of Arthur if they lived at the same time.