You meet Sherlock because you're a friend of John who got invited over for dinner with him and Mary because you just moved to London and he wanted to welcome you.
Sherlock Holmes was dying. His body slowly beginning to break down.
...
John Watson was an aspiring writer, but with a dark past.
...
"It's always the unexpected that change our lives."
Sherlock Holmes has always had a problem with illness ever since he was diagnosed with cancer when he was seven. After many years have passed Sherlock is now cancer-free and it isn't soon before he bumps into a man called John Watson. The two start to become close until old problems start to resurface and Sherlock starts having to fight for his life.