Utterson goes to visit his old friend Dr. Lanyon, who is dying. When Utterson comments on Lanyon's illness and brings up that Dr. Jekyll is ill as well, Lanyon says: “I wish to see or hear no more of Dr. Jekyll," and mentions that he considers Dr. Jekyll as "dead" to him. Dr. Lanyon then repeats that he doesn't want to hear any more on the "accursed topic."

This greatly surprises Mr. Utterson because the three men were the closest of friends when they were younger. He mentions to Lanyon that they are too old to form such strong friendships anymore. He wonders why Lanyon doesn't want to see Jekyll before he dies.

After Lanyon dies, he leaves a mysterious letter with Mr. Utterson, which is only to be opened after Mr. Jekyll dies or disappears. All of this fills Utterson with intense curiosity about what is going on.

Look at what Lanyon is doing in this chapter.  Isn't it strange and mysterious?

He is lying there terribly sick.  He says he is going to die and that nothing can be done to cure him.  It is apparently because of Jekyll that he is this way.

He says he has had a shock that is so terrible that he is happy to die.  He says that people would be more ready to die if they "knew all." He says he does not want to ever even speak of Jekyll again.

To me, this deepens the mystery.  What in the world could Jekyll have done?