Holmes and Watson are taking on Hydra in “Sherlock” Season 4…kind of. The PBS drama has cast a “Captain America” alumnus in the villainous role. Actor Toby Jones will be introduced as an adversary when the hit series returns.

It hasn’t been revealed exactly who Jones is playing, but the 49-year-old is familiar with portraying the bad guy. He starred as Arnim Zola, a Hydra doctor, in the first two “Captain America” films and he is also Dr. Jenkins/David Pilcher in “Wayward Pines.”

A villain can’t give away all his secrets though. Jones didn’t reveal any details about Sherlock (Benedict Cumberbatch) and Watson’s (Martin Freeman) new foe. “I'm excited and intrigued by the character I shall be playing in Sherlock,” Jones said in a BBC press release.

Executive producer Steven Moffat wouldn’t reveal the identity of Jones’ character, but teased that the actor would bring one of Arthur Conan Doyle’s victorian baddies to life. “Delighted to have Toby Jones on board, bringing to life one of Doyle’s finest villains,” Moffat added. Doyle wrote quite a few villains for Sherlock Holmes to outwit, so that doesn’t exactly narrow down the choices.

“Sherlock” Season 4 started filming in April, and the second episode starts production Monday. The season will consist of three 90-minute episodes. Although an abbreviated season likely won’t keep Sherlockians satisfied for too long, audiences know that they’re lucky to be getting more “Sherlock” at all. The series’ standalone special, which aired on on New Year’s Day, has been the only new episode fans have seen since 2014.

Moffat has previously said that “Sherlock” Season 4 will focus on the effects of people’s actions. “It’s consequences. Chickens come to roost,” Moffat told Entertainment Weekly in March. “It’s dark in some ways — obviously it’s great fun and a Sherlock Holmes romp and all that — but there’s a sense of… things… coming back to bite you. It’s not a safe, sensible way to live. It’s hilarious and exhilarating some days, but some days it’s going to be bloody frightening.”

“Sherlock” Season 4 is expected to air in winter 2017 on PBS.