Travis Fimmel, Jefferson Hall

"One must always think the worst, even of your own kin," advises wise boat builder Floki (Gustaf Skarsgård) in the opening moments of Vikings' Season 2 premiere. It's a warning Norse leader Ragnar Lothbrok (Travis Fimmel) must heed when his army faces off against that of his brother Rollo (Clive Standen) in a violent melee that has the 8th-century warriors fighting for their lives.

"There's going to be devastation," Standen teases during a break on set, deep in the Irish countryside. "This battle is the craziest thing that any of us has ever done on TV."

The bloody clash of kin was shot over four blazing-hot days last summer in an abandoned quarry with 236 extras and 105 stuntmen. And that's just a small taste of how much bigger the hit cable drama gets in Season 2. "The show knows what it is now," says executive producer Michael Hirst. "It's full of confidence, vigor and passion."

The History channel is feeling so confident about Vikings, in fact, that it is moving the series from its successful Sunday-night time slot to hyper­competitive Thursdays, beginning with the Feb. 27 opener. "With a lead-in of Pawn Stars, we know several million people are going to be poised to come into Vikings," says History's executive vice president of development and programming, Dirk Hoogstra.

If viewers aren't hooked by the big-budget battles, which intensify as the season continues, or the massive replica Viking dragon boats (the fleet has grown from three to eight and for the first time has sailed the open ocean), then the themes of ­romance, family and friendship should do the trick.

"Ragnar's got a lot of personal drama," Fimmel says. Topping that list is the love triangle featuring ­Ragnar, his shield-maiden wife, Lagertha (Katheryn Winnick), and Princess Aslaug (Alyssa Sutherland), who arrives unannounced, with a baby bump, courtesy of her affair with Ragnar in Season 1. Insulted and humiliated, Lagertha leaves the village until a major crisis forces her return. "She comes back stronger, better, fiercer," Winnick says. "She has power in her own right. I do much more battle work [this season]."

By Episode 3, the show has leaped ahead four years and we meet Ragnar and Lagertha's now-grown-up son Bjorn (The Hunger Games' Alexander Ludwig), who's intent on following in his father's heroic footsteps.

On set, the strapping Ludwig is even taller and more muscular than the formidable Fimmel. As they shoot a scene in which Ragnar tells Bjorn about a gruesome Viking execution method soon to be used on a traitor, the tension between father and son recalls Floki's warning to think the worst of your kin.

"Ragnar wants to take Bjorn under his wing and train him," Ludwig, 21, explains, "but he's a little threatened by the cub lion growing up and taking over the kingdom."

Bjorn isn't the only offspring who may be gunning for power. Four more Lothbrok boys are born this season, and although they are still babes, Ragnar already senses risk. He visits the Seer (John Kavanagh), hoping to hear that his children will be famous and accomplished — but that they won't outdo him.

For Fimmel, getting some on-screen dad time is a welcome relief from Ragnar's usual bloody fare. "My favorite scenes are the ones with the kids," he says. Later that day, he playfully coaches two toddler actors who are chasing each other around the set with wooden toy swords and shields. "Hey, Monkey Face!" he calls out, sending the tots — and Sutherland — into fits of giggles.

Ensuring that each Viking home is as happy and thriving as his own drives Ragnar to raid English territories ruled by King Ecbert (Law & Order: SVU's Linus Roache), who, like most of the show's characters, is based on a historical figure, a progressive who studied at the court of Charlemagne.

"Ecbert's a free thinker, and that makes him a real foe to Ragnar because he's not doing things by the book," Roache says. "They're two sides of the same coin. They've got an eye on the future and lead with vision."

Sharp as Ragnar's vision is, it might not be clear enough to see what's going on with his ally King Horik (Donal Logue), the rich and powerful man funding his raids. "Horik pits people against each other," Logue says. "Ragnar's a superstar — and ambitious. But Horik's a king — and cutthroat. There's not enough room for both of them."

Things may be crowded at the top, but the world of Vikings keeps expanding, with storylines about English politics (hint: We haven't seen the last of Ragnar's Season 1 nemesis King Aelle), religious cruelty and mortal danger for Ragnar's village.

Through it all, the onetime farmer excels at war, strategy and forging his own destiny. "By the end of Season 2," Fimmel says, "Ragnar gets a lot more control than what he had earlier, when he was fighting everybody all the time [without focus]."

Yet nothing is without a cost: "Ragnar helps his country," Fimmel says. "But he makes huge personal sacrifices."

Vikings returns Thursday, Feb.27 at 10/9c on History.

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