LONDON — Nearly a decade after his last science-fiction feature, 2015's The Martian, Ridley Scott is back in the genre with a dystopian thriller that the prolific director-producer and his starry cast say carries a message of hope.

The Dog Stars, the latest movie from the filmmaker behind Alien, Gladiator, and The Martian, adapts Peter Heller's 2012 best-selling novel of the same name and unfolds in a post-apocalyptic world.

Jacob Elordi stars as Hig, a mechanic who survived a pandemic that wiped out most of humanity — including his wife — and now holes up at an abandoned airport in Erie, Colorado, with his aging dog and Bangley, an ex-military man played by Josh Brolin.

Hig regularly sets off in an old yellow Cessna in search of other survivors and supplies, and eventually comes across a patchy radio transmission and the mountain hide-out of Cima (Margaret Qualley) and Pops (Guy Pearce) — where he finds both respite and trouble.

At the film's world premiere in London on Thursday, Mr. Scott said he jumped on the project after being sent screenwriter Mark L. Smith's adaptation. Smith's credits include co-writing The Revenant (2015).

"When I get science fiction which works on paper, you have to pay attention. I then react intuitively, and so when I'm half-way through a script like that I start to perspire in case the writer drops the ball. He didn't, so here we are," the 88-year-old filmmaker said.

"There have been so many zombie movies. There are no zombies in this," added Mr. Scott, who instead wanted to include optimism, which he called "essential."

The new film follows Gladiator II, his 2024 sequel to 2000's Best Picture winner Gladiator.

Most of The Dog Stars was shot on location in Italy, with production running multiple cameras.

"This was huge. Ridley is the king of epic, so everything was big," said Mr. Elordi, the Frankenstein and Euphoria actor, who relished the chance to "spend a lot of time outside" and to work alongside his canine co-star Rak Jasper.

"Rak Jasper has this incredible team of trainers that did all the work and I really had to just be there with a treat in my pocket," Mr. Elordi said.

Mr. Heller, whose novel marked his fiction debut, set no conditions on the big-screen adaptation and said he was "blown away" by the finished film.

"Cinema is a completely different discipline, it has its own demands," he said. "The power of the message that we have to keep our hearts open and take risks to love each other is in the movie and that's the main deal."

"It definitely centers on hope, human decency, human connection in devastating times," added Benedict Wong, who plays a member of a Mennonite community. "That's a leaf out of this book that we can all take and definitely something we really need in our times now."

The Dog Stars begins its global theatrical rollout, including in the Philippines, on Aug. 26, and carries an MTRCB rating of R-13. — Reuters