The “Sherlock” Season 3 finale, “His Final Vow,” introduces fans to a new enemy, Charles Augustus Magnussen (Lars Mikkelsen). As the promo video for the episode shows, Magnussen may be Holmes’ least favorite person in the world.

“I’ve dealt with murderers, psychopaths — none of them could turn my stomach like Charles Augustus Magnussen.”

Not only does Magnussen make Sherlock (Benedict Cumberbatch) nauseous, but the blackmailer also poses additional threats to Holmes. For one thing, Mycroft (Mark Gatiss) seems to be on the bad guy’s side — does Magnussen have something on Sherlock’s brother? There’s also the implied threat against Watson (Martin Freeman) and/or Mary (Amanda Abbington).

Could the upcoming Watson baby be in danger? Considering the title of the episode — foreshadowed in Sherlock’s final speech at the wedding — Holmes may find himself defending Watson with everything he has.

“His Final Vow” airs Sunday, Jan. 12 on the BBC and Sunday, Feb. 2 on PBS.