Nora Arnezeder, James Wolk, Billy Burke, Kristen Connolly and Nonso Anozie star in "Zoo"

In May, a tragic event at the Cincinnati Zoo sparked a worldwide discussion about animal behavior and shone a spotlight on modern zoos. As the debate rages on, a prime-time drama takes a fictional look at what happens when animals across the globe begin to display unusual behavior.

CBS's "Zoo" returns Tuesday, June 28, with a special two-hour season premiere. Based on the best-selling novel of the same name by James Patterson and Michael Ledwidge, the thriller follows a diverse group of people racing to unlock the mystery behind the pandemic before it's too late.

The first season was last summer's No. 1 scripted series, making it a shoo-in for a season 2 order, which was announced in October.

"'Zoo's' thrilling stories clicked with audiences each week during a very competitive summer," said CBS executive Glenn Geller in the season 2 announcement. "We're excited for viewers to see where our talented writers and cast take them as the adventure continues to unfold during season 2 in the ultimate fight of man vs. beast."

The series features an ensemble cast led by James Wolk ("Mad Men") as "renegade zoologist" Jackson Oz. In the first season, he uncovered a link between strange animal attacks and his late father Robert's radical theories about threats to humankind. He and his best friend, Abraham (Nonso Anozie, "Game of Thrones"), teamed up with French intelligence agent Chloe Tousignant (Nora Arnezeder, "Maniac," 2012) after Oz rescued her from a lion attack.

Oz also worked with news reporter Jamie Campbell (Kristen Connolly, "House of Cards") and quirky veterinarian Mitch Morgan (Billy Burke, "Twilight," 2008), who believe the strange animal behavior may be the result of a man-made mutation.

In April, sci-fi fans were buzzing with the news that "Warehouse 13" alum Joanne Kelly had signed on for a major role in "Zoo" for season 2. She'll play Allison, deputy secretary for the Department of Defense. Her character is said to have some history with Mitch, a fan favorite.

Two more new cast members are set to join "Zoo" this season. Josh Salatin ("Show Me a Hero") portrays a mysterious figure named Logan, who may be keeping a dangerous secret from Jamie. Alyssa Diaz ("Army Wives") plays Dariela Marzan, who's part of an elite military unit that encounters evidence of a troubling development in the animal mutation.

In the 13-episode first season, felines were some of the first animals to attack humans, followed by everything from bats to rats and even "man's best friend." Campbell quickly deduced that biotechnology company Reiden-Global was somehow connected to what was happening to the world's animals. After video surveillance footage showed escaped death row inmate Evan Lee Hartley (Marcus Hester, "Looper," 2012) leading a rogue wolf pack, Campbell found a photo of Hartley with Robert.

Kristen Connolly as seen in "Zoo"

What followed was a thrilling global race to find the culprit and the cure. Averaging more than six million total viewers per episode, the show was unquestionably a summer hit. However, it started off a lot stronger than it finished, with the premiere drawing about eight million viewers compared to the season finale's 4.81 million. In any case, CBS has put its faith in the series, despite lukewarm reactions from TV critics. While "Zoo" may have done fairly well with audiences, reaction from critics has been mixed, as it was for Patterson and Ledwidge's book. The TV series earned a 48 percent favorable rating from rottentomatoes.com, while metacritic.com rated it only slightly better with a 55.

Whether or not the critics approved, audiences earned the show another season. For anyone who may have missed the first season, don't worry -- "Zoo" has also joined the ranks of Netflix series, so there's still time to catch up. Last September, CBS announced that season 1 would soon be available in all Netflix territories, not only the United States.

With a mix of comedy, reality TV and variety running on the other major networks, "Zoo" doesn't have much direct competition for live viewers. ABC is going the sitcom route with "Uncle Buck" in the same time-slot while Fox presents the reality TV dating show "Coupled," and NBC has "America's Got Talent" and "Maya and Marty" on Tuesday evenings.

As for other summer dramas, ABC prime-time soap "Mistresses" slipped in the ratings last season, making it less of a threat to "Zoo." Fox's period drama "Houdini & Doyle" hasn't managed to come close to the CBS show's freshman numbers, so it would have to pull a real rabbit out of its hat to be a contender, as is the case with the network's "Wayward Pines." First-season ratings for NBC's David Duchovny vehicle "Aquarius" plummeted from more than five million viewers for the premiere to just over one million for the season finale, so it doesn't seem to be a danger, either. It's too soon to tell, but "Zoo" may actually face the stiffest competition from fellow CBS drama "American Gothic," which premiered last week.

Poised to dominate summer once again, "Zoo" is worth a look. To find out what happens next, tune in to the two-hour season premiere of "Zoo," airing Tuesday, June 28, on CBS.