Have you ever read a book that's hard to tell people about without giving away some of the plot? I recently finished Project Hail Mary by Andy Weir and couldn’t wait to recommend it. But as soon as I started talking about it to some colleagues, I realized there was a problem: there was no way to explain why I liked the book so much without spoiling one of its big surprises.

Here’s what I can say without ruining anything for you: Project Hail Mary is the latest novel by Andy Weir, who is best known for writing The Martian. It tells the story of Ryland Grace, a high school science teacher who wakes up alone on a spaceship in a different star system with no memory of how he got there. He quickly figures out that he’s been sent on a mission to save our solar system from a microorganism called the Astrophage, which is essentially eating our sun. If Ryland doesn’t succeed, the Earth will enter a new ice age that kills billions of people.

The twist comes about a quarter of the way into the book. So if you want to go into it blind, you should probably stop reading this now. I won’t ruin the ending or anything like that, but I’m going to give away a bit more than the summary on the book jacket.

It turns out that Ryland isn’t the only one looking for a way to stop the Astrophage. He crosses paths with an alien that looks like a Labrador-sized spider made out of rock. The rest of the book is about Ryland and his new alien friend—whom he not-so-cleverly names Rocky—working together to save their home planets.

Weir offers a somewhat plausible notion of what it would be like to make first contact. Unlike the humanoid extraterrestrials you see in a lot of science fiction, Rocky is completely alien in every sense of the word. He breathes ammonia, uses echolocation to “see,” and speaks using musical notes. Ryland has to create a smart bit of software before they can communicate. The two end up bonding over being lonely travelers who are light years from home, and they develop a beautiful friendship despite being so different from one another.

As I was reading about Rocky, I couldn’t help but think about Nick Lane’s excellent book The Vital Question. Lane helps you understand the extraordinary number of things that had to line up perfectly to create complex life on Earth. The odds that there is another sentient species relatively nearby seem low. (Rocky is from the 40 Eridani system, which is “only” 16 lightyears away from our sun.) Still, it’s exciting to think about what other life might be out there.

Like Weir’s other books, Project Hail Mary is clever about the dilemmas the hero gets put into. Ryland is a fundamentally decent and likable main character who you can’t help but root for. Because he has amnesia at the beginning of the book, you get to puzzle out what’s happening along with him, which is a lot of fun. He also has a great sense of humor. When Ryland realizes he’s about to become the first human to meet an alien, he thinks, “If there is hostile intent, what would I do about it? Die. That’s what I’d do. I’m a scientist, not Buck Rogers.”

He reminded me a lot of Mark Watney, the protagonist in The Martian. The two books deal with similar themes about how people work together in challenging situations, although the big difference with Project Hail Mary is that not all of the collaborators are human. I loved reading about how Ryland and Rocky combined their species’ expertise to solve problems they wouldn’t have been able to tackle on their own.

I thought some parts of the story—like how Ryland gets picked for his mission and how powerful the United Nations task force that organizes his mission is—were a bit unbelievable. They didn’t bother me too much, though. Science fiction gets a lot of latitude to conjure things up. It’s hard to be too distracted by something being implausible when you’re reading a story about a giant space spider.

I recommend the book for anyone who is in the mood for a fun diversion. I started it on a Saturday and finished it on Sunday, and it was a great way to spend a weekend. Even if you aren’t a big science fiction fan, Project Hail Mary is a terrific story about two friends using science and engineering to save the day.