"What people are responding to in this movie is how deep it is, how many levels it touches on, and how, in old-timey western package, it packs in a lot of more modern thoughts and feelings," said Mulroney.
The movie involves a young man out to avenge the murder of his parents. But in the process, he finds love and hope.
"Long Shadows" is also the feature film directorial debut for William Shockley, perhaps best known for his work as an actor on the TV western medical drama, "Dr. Quinn, Medicine Woman." He shot the film in Tucson with several crew members he's worked with for years, creating a real family atmosphere from the get-go.
"So, the actors that came in were really walking onto a very loving set, and then if you hire good human beings who happen to be brilliant actors, you're even luckier. And that's what we got," said Shockley.
That included Dominic Monaghan and Jacqueline Bisset.
"And she said to me, 'I've always wanted to play a cockney bad person.' So she was thrilled to play the villain," Shockley said.
Dermot was attracted to the idea of redemption in this movie for the main character, beyond what you'd see in a typical western.
"Processing trauma in your childhood trauma as a young adult. So, it's got a lot of depth and beauty," said Mulroney.
Early next year, Dermot will find himself in the real western community of Pioneertown, just outside of Palm Springs.
"My band, my country band, the duo with my brother, Kieran Mulroney, it's called Jackrabbit, plays at Pappy & Harriet's in Pioneertown Jan. 3, 2026 -- Jackrabbit, Pappy & Harriet's!" said Mulroney.
You can see Dermot in "Long Shadows" in theatres now.