Sherlock will get a visit from an old friend, his former drug dealer from London! TV Guide learned that actor John Hannah has been tapped to play the part. Hannah will play Rhys, who comes to New York seeking Holmes' (Jonny Lee Miller) help.
Here are more spoiler its from showrunner Rob Doherty:
"Rhys was a guy who had his finger on the pulse of crime in London. That's all in the past.
When we meet him in the present, he has sought Sherlock out because several years ago he saw an opportunity to retire from the business: He ripped off his bosses and made off with about $2 million and retired to Thailand. His daughter, who actually lives in New York, has been abducted and is being held for ransom. He comes to Sherlock because even Rhys understands and appreciates that on drugs or off drugs, Sherlock Holmes is the greatest detective in the history of detecting."
'Elementary' airs every Thursday on CBS.