The Sign of Four is a fascinating addition to the Holmes stories, giving us fresh insights into each of the characters and their stories. Here are some key events that add layers to the series as a whole.

One key event is in the very first scene, where we find Watson observing Holmes indulging in his cocaine habit. As a doctor and a friend, Watson is concerned and disgusted by Holmes's habit, and he is distressed at Holmes's apathetic response to his attempts to cure him of it. Holmes, on the other hand, is unmoved, and he denies being actually addicted to cocaine, attributing his usage to the absence of a mentally stimulating case. This sets us up to understand both the doctor's continuing concern for his friend's health and Holmes's unusual views of his own drug usage.

Another key event is the introduction of Miss Mary Morstan, Holmes's client who eventually becomes Watson's bride. Throughout the books, Watson repeatedly falls mildly in love, but it is the gentle and pretty Mary Morstan who finally claims his heart and his hand. Her appearance in the chronicles adds another layer to Watson's story and gives us a bit of insight into his character as well as hers. We find neither Watson nor Mary are mercenary people, as they are both more relieved than anything to find that the chest, which was supposed to make Mary "the richest heiress in England," is in fact empty.

Other key events that give us some insight into Holmes's character occur when we see his deductive reasoning in action. In the beginning, we see him idly deducing precisely where Watson has been that morning and describing the origins of his watch out of sheer boredom. Later in the book, we see him put those same skills into action on more important matters, such as the examination of footprints (during which he deduces that one set was made by a man with a wooden leg, and the other by a very agile, barefoot man, whose footprints are stained with creosote) and his discovery of the poisoned dart in Sholto's scalp.

In this book we also see Holmes using his clever disguises (he disguises himself as a sailor to search for the Aurora), and we are given a glimpse into how his Baker Street Irregulars operate.

The Sign of Four by Sir Arthur Conan Doyle is a novel featuring the detective Sherlock Holmes and his associate Dr. Watson. The novel begins when the woman Mary Morstan engages Holmes to help her with a double mystery, the disappearance of her father and the annual arrival each year of a valuable pearl from an unknown benefactor. 

The next key event is Holmes and Watson accompanying Mary to meet her mysterious benefactor, Dr. Thaddeus Sholto, who tells them of much earlier events. The major ones were Morstan and Major Sholto obtaining a fortune in India, the accidental death of Morstan, Mary's father, and Major Sholto's death.

The next key event is the murder of Thaddeus Sholto and the efforts of Holmes to discover the identity of his murderer. Next, Holmes locates and chases down Jonathan Small and his associate Tonga, the murderer. Small, rather than give up his treasure, throws it in the river.

The final key event in the novel is Watson proposing to Mary, and her accepting his proposal. 

What are the key events of Chapter Seven in The Sign of Four?

In chapter 7, several key clues are provided that foreshadow the solving of the crime. First, and most importantly, Holmes and Watson discover several small footprints left when one of the criminals stepped in a patch of creosote. The important fact in this instance is that the footprints are small. Second, Holmes discovers several small "spines of dark wood" that Holmes deduces to be poisonous. These two important clues will play a pivotal role in the famous chase seen on the Thames River in chapter 10.

Holmes also explains to Watson that even if he did not have the clue of the creosote footprints, he would still be able to solve the crime based on his ability to trace the criminals with other data at his disposal. Watson is skeptical of this, but is enlightened by Holmes' explanation of what transpired before and during the crime. His boast is born out at the end of the chapter when Toby, their tracking dog, ends his chase of the small-footed person at a barrel of creosote in a sawmill yard!

What are the key events of Chapter Seven in The Sign of Four?

Chapter 7 of The Sign of Four is called "The Episode of the Barrel." Watson realizes the depths of his feelings for Miss Morstan but dares not make them known for fear that he could be seen as preying on an heiress in a time of trial for her. He escorts her to the home of Mrs. Cecil Forrester.

Watson reflects on what he and Holmes have observed and learned so far in the case and laments that the overall situation has become murkier, not clearer, to him. Watson picks up the dog, Toby, that Homes wanted from Mr. Sherman and takes him to Pondicherry Lodge.

Watson and Holmes determine how access was gained to Sholto's bedroom, and Holmes finds a pouch of darts on the roof. Holmes dabs a bit of creosote from the footprint, and he uses Toby to track the man who left it. However, Toby leads Holmes and Watson only to more creosote.

Nonetheless, Holmes has deduced that the wooden-legged man Jonathan Small needed an accomplice to perform the murder because of his disability.

What are the key events of Chapter Seven in The Sign of Four?

Chapter Seven of The Sign of Four begins with Watson escorting Miss Morstan home and then meeting with Holmes in Pinchin Lane, as previously agreed. Throughout the rest of the chapter, there are a number of key events which contribute to Holmes making his great hypothesis about the murders. 

First of all, Holmes traces the murderer's footsteps to ascertain how he gained access to Sholto's bedroom. Next, he employs a sniffer dog called Toby to track the scene of creasote which Holmes found on a handkerchief. This takes Holmes and Watson on a "six mile trudge" across London but it yields important results. 

After these two events, then, Holmes delivers his hypothesis to Watson. This is a turning point in the novel because it demonstrates Holmes's powers of deduction and drives the plot to its great climax. As he explains to Watson, Holmes has now fathomed that the "wooden-legged man" is, in fact, Jonathan Small, whose name appeared on a map that Miss Morstan had in her possession. From his foray on the roof, Holmes deducts that Small needed the help of another man to ascend Sholto's house and that it was this man, Small's associate, who committed the crime. 

Armed with his thorough understanding of what has passed, Holmes now warns Watson of the potential dangers of locating Small and his associate. He asks Watson if he has his pistol while preparing his own revolver for action. By this time, the dog, Toby, has completed his journey across London and this sets the scene for the next chapter of the book and, more importantly, the pursuit of Jonathan Small.