October 12th

Holmes,
I had the most intense adventure today. Having just sat down to write to you, I reached over to get a pen when I spotted an earwig crawling on my pillow. Quite disgusting. But I disposed of the little vermin and will hopefully get some sleep tonight.
I received your letter early this week. I wish I could say that I haven't had time to respond, but the truth is that I have simply been too lazy. I do feel a bit guilty about that. 
I assume that by now Lestrade has visited you. Please do give me whatever news you can. As... interesting as our adventures have been and no matter how distressing, disturbing or dangerous, I must admit that I do not like the thought of you alone in the city with all those criminals and no one to pick up after you.
On that note, I am finding my time in the country very relaxing. You must remind me to thanks your brother for the lend of his property. I also thank you, Sherlock , for recommending that I take some time to relax. I must confess that our latest case taxed me more than I could have  foreseen. It must have been that bizarre and entirely unforeseeable explosion at the docks. But even I can see that Blackwood was... well, the world is well rid of that man. 
Now, as you know, Mary had originally planned to come with me. Due to a rather unfortunate series of events, however, she is as of yet unable to join me. But I do hope that she will be here within the week. 
I have been spending my free time on the grounds, fishing and compiling my notes on our latest adventure. 
I hope this letter finds you well and that you have managed to keep the flat standing. I don't want to visit and find that you've demolished the place. 
Remember to write my soon with news from Lestrade.
-John Watson
P.S. Remember your revolver.

Watson,

My dear friend, I don't have much time. A series of events has taken place and they are of the utmost importance. I write to you from the city, hoping that adventure still catches your eye.

The details are unraveling slowly, but I trust as I send them your way that you will find no objections in joining me on this case.

Lestrade is coming this morning with more details on the matter and I will be sending you the next letter as soon as the data has revealed itself.

I hope all is well, ol' boy, and hope to hear from you soon! Until then, let us keep in mind that the game is afoot!

--Holmes