(CNN) -- It was one of the hottest films out of Sundance, but "Blackfish" will leave you with chills.
The nearly 90-minute documentary tells the story of SeaWorld trainer Dawn Brancheau, who was killed in 2010 when the killer whale Tilikum grabbed her and yanked her underwater.
"I became interested in this project when I found out about the death of Brancheau," filmmaker Gabriela Cowperthwaite said. "I was very confused by that story, because I didn't understand why a killer whale who was a very highly intelligent animal would have made a decision to kill a trainer that was actively feeding it."
The result of Cowperthwaite's curiosity is a film that raises a number of questions, not the least of which being whether killer whales have any place in theme parks.
Critics have praised "Blackfish" for being an "emotionally powerful" and "mesmerizing psychological thriller" that could double as a teaching tool. The documentary arrives in select theaters on July 19, and it will also air on CNN as part of CNN Films on October 24 at 9 p.m. ET.
To unravel what happened between the 12,000 pound Tilikum and Brancheau, Cowperthwaite also takes us through the 39-year history of orcas in captivity. Although Brancheau's story is at the heart of the film, "Blackfish" also shows more generally the dangers of working with orcas and their majestic beauty and intelligence.
"For anyone who has ever questioned the humaneness of keeping wild animals in captivity and training them to perform tricks for food, this will be trenchant, often harrowing stuff," The Hollywood Reportersaid in its Sundance review. "Perhaps even more so for those who have never considered the issue."