Indy and Herman are still attending Charenton Academy in England as their fathers work in-country, as previously seen in The Ghostly Riders.

On page 11, Indy reflects on the times he fought grave-robbers in Egypt, thieves in America, and had once fallen into a boxcar full of snakes. "Grave-robbers in Egypt" is likely reference to Tomb of Terror (and/or "My First Adventure", though episodes of The Young Indiana Jones Chronicles did not appear until 1992, two years after the publication of this novel) and "a boxcar full of snakes" to "The Cross of Coronado". I'm not sure what "thieves in America" refers to, though it might be argued within continuity that it refers to the French novel The Metropolitan Violin, published much later in 1997.

On page 12, Herman is said to wear glasses, though he is not said to wear glasses in any other stories. Perhaps he developed poor eyesight sometime after the events of "The Cross of Coronado".

Herman sarcastically refers to Indy as Henry Wadsworth-Jones on page 12. He may have been inspired by the name of American poet Henry Wadsworth Longfellow (1807–1882).

Herman Mueller, Sr. is on a dig just outside of the prehistoric monument of Stonehenge.

On page 13, Indy's father is said to be teaching at Cambridge University. But, in The Ghostly Riders (set in October 1913), it was Oxford University at which he was teaching. Did Henry, Sr. change his tenure in the middle of the semester??

Page 14 reveals that Herman Mueller, Sr. was not a professional archaeologist, but he was a wealthy amateur who had made many finds that now were displayed in museums.

On page 22, Herman has a copy of Boy's Own Adventure Magazine featuring the story of "The Phantom of Fenley Marsh". These appear to be a fictitious magazine and story. The title of Boy's Own Adventure Magazine is likely inspired by The Boy's Own Paper, a British story paper published from 1879-1967.

On page 23, Indy comments on Herman's perpetual candy supply. Herman's penchant for carrying candy around is also noted in The Phantom of the Klondike.

Indy and Herman get off their train at Amesbury. This is the town in which Stonehenge is located.

On page 26, Mr. Mueller drives a Model T Ford that came with the house he's renting in Amesbury. Herman says they have a Pierce-Arrow back home. The Pierce-Arrow Motor Car Company operated from 1901-1938 and was known for its luxury vehicles.

The discussion of the origins of Stonehenge among Mr. Mueller, Professor Jones, and the two boys is largely accurate of the various theories of the time. Some believed it was constructed by ancient Druids, while many experts said the builders remained unidentified, which largely remains true today. Parts of Stonehenge are orientated towards the midsummer's solstice, just as mentioned by Mr. Mueller here. The Slaughter Stone mentioned by Professor Jones is also an actual part of Stonehenge, some researchers believing it had been used for animal sacrifice; human sacrifice was probably not practiced, despite the professor's opinion here (and Indy's vision later on). Other researchers believe the so-called Slaughter Stone is just a fallen upright stone.

On page 32, the Muellers and Joneses receive a rude message via a stone thrown through a window, wrapped in the Stonehenge article torn from the Encyclopedia Britannica.

On page 35, the Muellers and Joneses ride over the gently rolling land of Salisbury Plain. Stonehenge is located on this plain.

The Altar Stone mentioned on page 38 is an actual part of Stonehenge.

Harry Stone tells Indy and Herman that some say that Merlin brought the megaliths of Stonehenge from Ireland. This is one of the stories of Arthurian legend.

On page 41, Harry refers to Sir Pengrave as Squire Pengrave. The term "squire" came to be the title of the village leader in English life in the 17th Century onward. This man was usually the largest landowner in the area. The term has generally fallen out of use after the early 20th Century.

On page 52, Indy spies Russell's Public House in Amesbury. This appears to be a fictitious establishment for Amesbury. The Slaughter Stone inn on the next page also appears to be fictitious.

On page 67, the Arch-Druid says he will initiate Sir Pengrave into the Upper Degree of the Black Druids tomorrow night at Warrior's Mound. The Black Druids appear to be a fictitious group, as is Warrior's Mound (at least by that name) on Salisbury Plain. 

Entering the Pengrave mansion on page 76, Indy expects Dracula to come leaping out of the shadows at any second. Count Dracula, of course, is the classic vampiric character from Bram Stoker's 1897 novel Dracula.

Ritter chases Indy in a Benz automobile. The modern day automobile manufacturer is Mercedes-Benz.

On page 80, Ritter says, "Wo ist--?" This is German for "Where is--?"

On page 95, Ritter and another German agent, Hans, whip out Luger pistols. The Luger was designed in 1898 by the Austrian Georg Luger. It was in service in various world militaries from 1900 into the 1970s.

On page 96, Count Von Pappendorf mentions the Middle Ages magician Paracelsus. Paracelsus (1493–1541), was a Swiss alchemist, philosopher, physician, and theologian of the German Renaissance. Some of the skills he learned were considered "magic" by some who lived at the time.

On page 104, Sir Reginald mentions Scotland Yard. Scotland Yard is the name for the headquarters building of the Metropolitan Police of London.

On page 106, Herman's father proclaims that he has been a member of the American Friends of Germany, but will be no longer after learning of the German spy ring in Britain. The American Friends of Germany appears to be a fictitious organization of the time, possibly inspired by the real world Society of American Friends of Germany established much later in 1933 to support the cause of the German Nazi party.

On page 116, Von Pappendorf says, "Vas ist--?" This is German for "What is--?"