TV THIS WEEK: Crisis on Infinite Earths begins, A Charlie Brown Christmas and more

It's been a long time coming, but The CW's biggest super-crossover is finally here: Crisis on Infinite Earths. But that's not the only geeky thing to watch on TV this week.

Yes, Crisis has arrived to decimate the multiverse, but we'll have to wait until Sunday to get a look at all that craziness. Before then, Arrow and The Flash are still new as they look to wrap up some pre-Crisis stories (most notably The Flash's Bloodwork arc), along with Black Lightning as he prepares to crossover with the wider universe for the first time. If that's not enough Arrowverse, The CW will also be hosting a post-Crisis after-show with Kevin Smith.

Outside the super-shows, HBO has new installments of His Dark Materials and Watchmen; SYFY has a new Van Helsing; and ABC has its annual airing of A Charlie Brown Christmas to get you into the holiday spirit. If you're looking for a bit of action, USA has new episodes of Treadstone and The Purge. History Channel's Vikings is also back for more butt-kicking action.

Check out the full rundown below and let us know what you'll be watching.

HIGHLIGHTS

The Flash (The CW), Tuesday 8PM - "The Last Temptation of Barry Allen, Part 2"

With The Flash freshly infected by the monstrous Bloodwork, Iris and Cisco battle to help Barry take control of himself before he's lost forever to Ramsey's influence. Meanwhile, the rest of Team Flash fight to reclaim control of Central City from Bloodwork's growing army.

Vikings (History), Wednesday 9PM - "New Beginnings/The Prophet"

Bjorn struggles with the responsibilities of kingship and finds he can't rely on his mother, Lagertha, she has other plans; Ivar falls into the hands of the Kievan Rus, and in their ruthless and unpredictable ruler, Prince Oleg, he may finally have met his match.

A Charlie Brown Christmas (ABC), Thursday 8PM

In the Emmy and Peabody-winning animated cartoon from 1965, the gang mounts a holiday pageant as Charlie Brown bemoans Yuletide commercialism. Also: a new set of animated "Peanuts" vignettes, based on previously published strips. Voices...Charlie Brown: Peter Robbins. Lucy: Tracy Stratford. Linus: Christopher Shea.

Van Helsing (SYFY), Friday 10PM - "All Apologies"

Now that Violet knows where the three pages are, she returns to Fort Collins with Axel and Julius.

Supergirl (The CW), Sunday 8PM - "Crisis on Infinite Earths: Part One"

The Monitor sends Harbinger to gather the worlds' greatest heroes -- Supergirl, The Flash, Green Arrow, Batwoman, White Canary, The Atom and Superman -- in preparation for the impending Crisis; Lena must find a way to save the people of Earth-38.

MONDAY

Black Lightning (The CW), Monday 9PM - "The Book of Resistance: Chapter Three: Battle of Franklin Terrace"

Black Lightning goes up against the ASA. Meanwhile, Tobias continues to manipulate Lynn.

His Dark Materials (HBO), Monday 9PM - "The Lost Boy"

The alethiometer sends Lyra and Iorek on a new path, leading to a shocking but vital clue.

TUESDAY

The Flash (The CW), Tuesday 8PM - "The Last Temptation of Barry Allen, Part 2"

See more in our "Highlights" section above.

How to Train Your Dragon: Homecoming (NBC), Tuesday 8:30PM

Hiccup and Toothless share stories of their special relationship with their respective families as they prepare for the Snoggletog Festival.

Arrow (The CW), Tuesday 9PM - "Purgatory"

Oliver's mission takes him to Lian Yu where he tries to ignore the repercussions of the looming Crisis until he receives help from an old friend. Meanwhile, a united Team Arrow faces a recognizable villain.

The Purge (USA), Tuesday 9PM - "Before the Sirens"

Purge Night looms. Ryan and Esme put a plan in motion. Marcus readies for a showdown. Ben spirals.

Treadstone (USA), Tuesday 10PM - "The McKenna Erasure"

Doug tries to save a target. Edwards and Haynes are hunted. Soyun goes undercover.

WEDNESDAY

Riverdale (The CW), Wednesday 8PM - "Chapter Sixty-Five: In Treatment"

The residents start getting mysterious videotapes delivered to their homes; The Riverdale High seniors wait for their college acceptance letters; The school's guidance counselor set up a meeting with the group to know what's bothering them.

Vikings (History), Wednesday 8PM - "The Saga of Floki"

Ivar the Boneless has left Kattegat, on a journey to parts unknown. He encounters a stranger and is flooded with memories of his past, prompting Ivar to recount the saga of the enigmatic genius, Floki.

Nancy Drew (The CW), Wednesday 9PM - "The Path of Shadows"

Nancy and the crew learn the car wreck that left one of their own at death's door was no accident. While simultaneously hoping to solve the crime, the crew investigates the physical evidence of sabotage to the car and take a supernatural detour into the metaphysical world.

Vikings (History), Wednesday 9PM - "New Beginnings/The Prophet"

See more in our "Highlights" section above.

THURSDAY

A Charlie Brown Christmas (ABC), Thursday 8PM

See more in our "Highlights" section above.

A Saturday Night Live Christmas Special (NBC), Thursday 8PM

Holiday-themed comedy from "Saturday Night Live" is featured.

Supernatural (The CW), Thursday 8PM - "Last Call"

Dean goes off on his own to take on a case; and Castiel has an idea of how he can help Sam track down God.

Evil (CBS), Thursday 10PM - "Exorcism Part 2"

David is shocked to learn he is being sued for inflicting severe psychological harm on Caroline Hopkins, after he assisted in her exorcism. The accusation leads him to question his future as a priest, especially once he develops a very close connection with his defense attorney, Renee Harris.

FRIDAY

Charmed (The CW), Friday 8PM - "The Rules of Engagement"

Maggie makes a life-changing decision that her sisters and Harry fear will destroy her.

Van Helsing (SYFY), Friday 10PM - "All Apologies"

See more in our "Highlights" section above.

UFOs: The White House Files (History), Friday 10PM

From Truman to Trump, there has been a legacy of secrecy and controversy surrounding UFOs and extraterrestrials. In fact, Eisenhower, Nixon, Carter, and Reagan are each rumored to have had personal encounters. Could these powerful leaders be hiding the truth about UFOs from the public? Or is it possible that some Presidents are kept in the dark because they can't be trusted? Whatever the case, these dark secrets about UFOs are likely to be found in the White House Files.

SATURDAY

Ancient Aliens: Declassified (History), Saturday 8PM - "The Cosmic Connection"

Throughout the ancient world, structures were built to mirror the constellations in the night sky; a look at if its possible these structures were designed as messages for extraterrestrial visitors.

SUNDAY

God Friended Me (CBS), Sunday 8:30PM - "High Anxiety"

Miles decides to walk away from the account after helping one last friend suggestion, a window washer with a sick daughter.

Supergirl (The CW), Sunday 8PM - "Crisis on Infinite Earths: Part One"

See more in our "Highlights" section above.

Crisis Aftermath (The CW), Sunday 9PM - "Episode 1"

A celebration of the massive DC crossover event "Crisis on Infinite Earths." Superfan and frequent series director Kevin Smith hosts this special behind-the-scenes look at every angle of the explosive crossover event.

Watchmen (HBO), Sunday 9PM - "A God Walks Into a Bar"

Angela's mysterious past in Vietnam is at last revealed.

Mr. Robot (USA), Sunday 10PM - "410 Gone"

Fans like Dom and Darlene.

*TV listing information via TV Guide, Zap2it.