Dr Jekyll and Mr Hyde - Chapter 6 - Incident of Dr Lanyon

Mr. Hyde has disappeared, and Dr. Jekyll has emerged from his seclusion, becoming more active in society and charitable works. However, Mr. Utterson, a lawyer and friend of both Jekyll and Lanyon, notices that Dr. Lanyon's appearance has deteriorated rapidly and that he seems to be terrified by something. Lanyon tells Utterson that he has had a shock and that he is a doomed man, refusing to speak about Jekyll. Utterson writes to Jekyll, asking about the situation, and Jekyll responds cryptically, stating that he and Lanyon will never meet again, and that he will lead a life of extreme seclusion. He also hints that he has brought on a punishment and a danger that he cannot name. 

Utterson is left with a letter from Lanyon that he cannot open until the death or disappearance of Dr. Jekyll.  making the situation even more mysterious. What could Lanyon possibly have written? Will it explain all the strange events?