In the episode, Watson had disappeared, and Mary goes to Holmes hoping to find him there, but when he confirms that he has not seen him in weeks, Holmes begins an investigation to track Watson down, assisted by Mary. Their quest helps develop Mary's own flair for detective work.
Now, the reason behind this happening is that this was shot in late 2011 through 2012. I was nowhere near as experienced as I am now, and so there are going to be things that are nowhere near what I can do now. But these remastered versions will benefit from this experience with such things as upscaled resolution, brighter looking colours, and far faster pacing.
Not everything is fixable or changeable, but I do feel that it is largely improved as a whole (though, the latter episodes have been able to be restored a lot more). All of which will hopefully make them more palatable for first time viewers who check out the early stuff first! Or for old time fans that fancy a rewatch. Hope that you enjoy.