In “The Adventure of the Engineer's Thumb,” Victor Hatherley relates his stunning and nearly deadly adventure to Sherlock Holmes and Dr. Watson. As Hatherley tells his tale, we are given several clues that things are not at all as they seem, and that Colonel Stark and his story are both as false as can be.
Our first clue that something is amiss is that Stark is looking for a hydraulic engineer who can keep a secret. This should make Hatherley run the other direction as fast he can, especially when Stark also notes that Hatherley has no wife or living parents. In other words, there is no one to miss him. What's more, Stark insists that he and Hatherley travel at night to go look at the press that is acting up. Hatherley really should know better than to go with this man, but the offer of fifty guineas is far too tempting.
Hatherley gets another clue that something is wrong when Stark tells him that he is pressing fuller's earth. No one actually uses a press on fuller's earth, and Hatherley knows it. Stark merely says that they have their own process, and again Hatherley goes along. The money calls.
The secrecy involved in the carriage ride (the carriage is completely sealed, and Hatherley cannot see out) is another tip off as is the creepy, silent house and the warning from the woman with an accent. Hatherley really should have run for his life at this point, but he looks at the press (which is strangely inside the house; it is clearly not used for fuller's earth) and tells Stark what is wrong and how to fix it. Within the press, Hatherley sees metal residue, and this makes him even more suspicious.
Unfortunately for Hatherley, Stark senses his suspicions and tries to kill him, first by locking him in the press and then by attacking him with a cleaver. Thankfully, the woman rescues Hatherley, and he only loses his thumb instead of his life.
Holmes recognizes a case when he hears one and goes with Hatherley to the house. Another young engineer has recently disappeared in the same area. When they arrive, the house is on fire, and Stark and the others, who are actually counterfeiters, are gone. Hatherley never gets his money, but at least he has escaped with his life.