The film opens with detective-for-hire Sherlock Holmes (Robert Downey Jr.)
and Dr. John Watson (Jude Law) in the middle of their adventuring
years. After closing their latest case with the capture of a murderous
occultist known as Lord Blackwood (Mark Strong), Holmes and Watson are
thrown back into the mix when Blackwood mysteriously returns from the
grave with a plot to take over England. Meanwhile, career thief Irene
Adler (Rachel McAdams)
arrives in town asking for Holmes’ help with a related matter, but
whether or not she’s a friend or foe is uncertain. And to make matters
worse, Holmes might just have to do it all on his own, because Watson
has decided to up and quit the business for a shot at married life.