Now, here’s a rare situation. One of the strengths of the gamebook genre is in the sheer variety of situations it covers. Unlike most RPGs, there aren’t a lot of expensive assets that need to be built and hopefully reused in future games, since apart from a handful of still pictures, the world is built through text. This frees the writers to tackle any kind of story or setting they want, including superheroes, pirates, horror, fantasy, comedy, and so on. With virtually anything on the table in terms of possibilities, the one type of story we don’t see terribly often in gamebooks is a sequel story. Sure, the Fighting Fantasy series had a couple of direct sequels along with some tenuous links between their fantasy stories, most notably in the Sorcery! sub-series, and even the classic Choose Your Own Adventure series had a couple of follow-up books to some of the most popular stories. The Lone Wolf series was notable for allowing you carry your character forward from book to book, though the stories necessarily had to be stand-alone to a great extent.

Generally, though, sequels aren’t done. They’re tricky, since you have to either take all the player’s choices and experiences into account, which is difficult enough in a video game but nearly impossible in a paper book, or you have to set down one single canonical sequence of events, which can be a turn-off in a genre that’s ostensibly all about player agency. Sol Invictus ($3.99), the sequel to last year’s rollicking sci-fi action story Heavy Metal Thunder ($3.99), handles things gracefully. Although there were many choices to be made in the original story, the author seems to guess that you’ll really only care much about one. It’s dealt with by a simple choice part of the way through the adventure. Everything else that happened is either vague or irrelevant enough that the writing can easily gloss over the finer points.

The game finds a way to strip your character of his inventory at the start, assumes you made it to level three in experience, and asks you to choose your skills and allocate your points fresh. It then dusts off its hands and gets down to the business of the current story. When we last left the protagonist, Cromulus, he had traveled a long way to rejoin his fellow Legion members, signed up with a unit known as the fanatics, and kicked some serious alien butt in a crazy jet-pack space battle, saving his mothership and dealing a powerful blow on behalf of the human race. Even though it was clearly just the introduction to the overall story, Heavy Metal Thunder felt epic in its scale and immensely satisfying. Sol Invictus tells a different kind of story, but it’s equally massive in its scope.

Until its climax, Heavy Metal Thunder was very much a solitary experience. Cromulus didn’t even have a proper name when we met him, nor did he remember much of his past. Most of the people he met along the way were duplicitous jerks at best and murderously hostile at worst. Survival seemed unlikely, without even so much as a proper direction to head in at times. Finding the mothership was like getting a gulp of air after being underwater for far too long, the final battle serving as a fantastic reward for living through it all. Well, in this story, that’s all turned around. Almost immediately, you’ll get to know your fellow unit members, and unlike the people we met last time around, you can trust each one of them implicitly. They’ll have your back, and you need to have theirs. You’re not wanting for a direction, either. Most of the time, you’ll have full knowledge of the overall plan and where you need to go, and if that’s not enough, your commanding officer will usually help clear things up.

Naturally, you can find yourself off the beaten path a little bit at times if you make the right (or wrong) choices. There’s quite a lot happening behind the scenes of the main story if you’re willing to look for it. You don’t have to, mind you. You can simply follow along the roller coaster ride of the main plot, killing Invaders, collecting critical equipment, and saving your fellow humans. You’ll certainly have a good time of it. If you do find some of the loose threads at the edge of the fun times, you’ll get hints at something darker going on, though resolution to any of those threads will escape you for now. Either way, if Heavy Metal Thunder was a story about getting to know Cromulus, Sol Invictus is a story about getting to know the universe he lives in, and there’s plenty here to merit going through the game several times just to fill in details.

Although the systems that govern the gameplay are the same as in the first game, the design of the adventure gives Sol Invictus a very different feel. Heavy Metal Thunder had a lot of random junk you could pick up and keep in your very limited inventory with no clue what you might end up needing it for. It was kind of fun to figure out where to use things, but it was also kind of frustrating because at times it felt like you were being punished for not being clairvoyant. Sol Invictus steers hard in the other direction. There’s almost nothing in the game to pick up except for items with a practical use. Anything that doesn’t fit into that category is meant to be sold off. Instead of having items gate your choices, your previous decisions serve the role. Who did you recruit on that one space station? Did you talk to this one person before? It’s a lot more organic, and it allows you to go hog wild filling your inventory with things you know you’ll need. Don’t forget to bring lots of ammo.

Another interesting thing is that due to the way the story is structured, you have the chance to make use of a shop between most of the chapters. Here, you can use the money you’ve earned to buy new equipment or supplies, giving you the opportunity to tailor your equipment to your needs rather than just rolling with what the game gives you. The game uses that currency to play with your decision-making. Sometimes you have the chance to make a few extra bucks by being more aggressive or sneaky, and following those roads can open up interesting new bits of story or close the door on others. Sol Invictus is a bit more challenging than the first game, so the temptation to gain every advantage can be quite a powerful influence on your choices.

One way the game stumbles in comparison to the previous title is in the climax. It’s exciting enough, but it feels a little anti-climactic compared to Heavy Metal Thunder‘s extremely strong finish. At least to me, the final conflict is overshadowed by more thrilling sequences earlier in the story. It doesn’t feel nearly as tense, and the stakes don’t seem as high. Still, it wraps up this chapter’s tale well enough, leaving enough unanswered questions to keep you interested in the next story. Cromulus’s work isn’t near finished yet, even after all he goes through in Sol Invictus, so I suppose we’ll just have to see where things go from here.

I should mention that like Heavy Metal Thunder, Sol Invictus is intended for adults. It makes liberal use of coarse language and some of the scenes it describes can be pretty grotesque. As the majority of gamebooks are all-ages friendly, I think the R-rated writing helps this series stand out, but its tone isn’t going to be for everyone. It’s largely well-written, but like the original book, it does sometimes come off like it’s trying a little too hard. That said, I really enjoyed the character work in this one, and the action sequences are once again compelling and exciting to read. I especially appreciate the way author Kyle B. Stiff is able to lace the text with just enough paranoia to keep you doubting just about everything and everyone. Perhaps more so than with any other gamebook I’ve played, I find myself resonating with the feelings and emotions of the lead character. He’s not a blank slate, but I don’t feel disconnected from him either.

If you enjoyed Heavy Metal Thunder, the sequel is a no-brainer purchase. It moves the story forward in all the right ways, fleshes out the fictional universe considerably, and provides many of the same thrills with fewer frustrations. It hits its peak a little earlier than it should, and there’s still a lot of questions left up in the air due to its position as a middle chapter, but overall, it’s a huge, dense adventure packed with action, interesting characters, and lots to discover. Sol Invictus follows more gamebook traditions than it breaks, so it’s probably not going to appeal to you if you’re not into the genre, but its unique tone and intriguing setting should captivate anyone else. I’m definitely looking forward to the next installment.