While a great DM can create an adventure on the fly out of a set of ragged note cards and carefully-chosen random encounters, most of us need a little more preparation -- and a lot more structure.
The hook gets the adventure started (as discussed in "Setting the Hook"), but the plot needs more than just a beginning; it needs a middle and an end as well. How can you build those and know they'll work? What are the best kinds of adventure plot structures?
Well, there are two standard ways to think about adventure structures: linear adventures and matrix plots. Likewise, there are two primary methods of advancing the plot: triggered encounters and site-based encounters. Both approaches have their strengths and weaknesses, and most adventures meld the two. Neither is strictly "better" than the other, but most DMs find they prefer one or the other.
The beauty of linear plots is that they work so simply, and any group of players, even complete novices, can succeed with it. The party goes through a set of encounters in sequence. These can be encounters sequenced in time or in space.
Chronological Linear Plots
Adventures that are linear through time include things like sieges, rebellions, regicides, or natural disasters, where the events unfold in a logical progression -- but the party either helps or hinders that progression. The party can act only when it has information to act on or when circumstances around the PCs change. As the DM is the gatekeeper of game information, you control the pace of the game. If the vital ship hasn't arrived yet, or the crucial message hasn't reached its recipient, the adventure doesn't progress. The party can make preparations, or do research, or go on other adventures -- but the chronological adventure moves when you say it does. This can be a great help if you are designing, say, an adventure with the first scene played at 1st level, the second major scene at 4th level, and the finale at 6th level, but it's an unusual way for most designers to work. Essentially, a chronological design like this is a one big set of linear triggered encounters (see below), and it's often more linear than it needs to be.
How can you tell that a chronological design might be too linear? The flow chart for the design doesn't branch anywhere; the party just waits for you to provide the action and responds. That sounds worse than it is; the level of control of timing can create memorable action, but it's not what most players think of as a "standard D&D adventure".
Geographic Linear Plots
Linear plots like this are usually either a road adventure or a dungeon. Road adventures or quest adventures are linear because the important encounters happen on a road, river, trade route, or other path. The Hobbit is a fine example, but Lord of the Rings is not because the party splits up and events happen in divergent locations that all affect the end result.
Dungeons are often touted as the perfect linear adventure, especially dungeons that contain choke points such as gates, single staircases, or air shafts that the party must traverse to reach the next section. And they are linear adventures, but in some ways they can often be bypassed by a clever party with disguises and stealth, with teleportation or other movement magic, or simply by digging a tunnel from one section of the dungeon to another. In most cases, dungeons are designed to offer at least a few branching paths for players to explore, to avoid being boringly linear.
Road adventures are really the most satisfying approach to linear adventures, at least for the DM. They allow a DM to showcase his favorite exotic scenery, to throw nuisance encounters at the party, and to grant or take away polders (discussed in Adventure Builder #1 and Dungeon 135). You have total control over the pacing. If you need an important NPC to show up early, just move him one day's travel closer to the party. If the party is too fresh or too stealthy, you can add a weather encounter, bandits, or even just an annoying group of zealous pilgrims who want to travel along with the party. If the party wants to complete the adventure, they have to follow the road. It's the perfect example of a railroad plot, with all its strengths and weaknesses.
The Trouble with Linear Plots
So if linear plots are so wonderful from the DM perspective, why doesn't everyone use them? Well, they do, in books and movies, where the narrative is presented complete and whole and the reader or viewer just soaks it in. But players want to feel a sense of mastery and control: what's the point of being a big shot hero if your actions don't matter and your fate is already totally determined? No group of players wants to walk through a completely linear A-B-C sequence of rooms that ends with some big mastermind encounter. It's logical, it's a progression of suspense and tension, and it's totally unsatisfying. Players want to see their choices (or at least the illusion of choice) affect the gameplay.
So, linear adventure designs need to manufacture the illusion of choice.
The illusion of choice is just what it sounds like: no matter what decisions the players make, they wind up where you want them to wind up. All NPC wizards can translate the Lost Book of Golgamar. Some dungeon caverns are red herrings but the only way to the second level leads through the big boss's room. All taverns contain one of the cardinal's spies. All roads lead to Mount Doom. It doesn't matter what they choose.
But of course, it should never look that way. To the party, choices should matter, and if you hint otherwise, players have every right to be annoyed and frustrated with your game. If you give them nothing but tactical combat choices to make, you might as well be playing a miniatures wargame. They need to have at least some control.
Even if choice is an illusion in your design, it shouldn't always be an illusion of success. Some of their false choices should appear to be failures. But better yet, your adventures shouldn't be entirely linear. They should contain branching or matrix elements as well.
Matrix plots are looser plots that don't progress from A to B to C, but may jump around in any order. Three factions fight for dominance in Sigil, the City of Doors, and the PCs may align themselves with one or more of them. A plague threatens a kingdom, but the clues that point to the culprit can be found in any order. Matrix plots may move ahead over time with or without the PCs' input. They are more typical for mystery adventures, city adventures, and horror adventures.
Matrix adventures depend on triggered encounters or site-based encounters. These correspond to the basic encounter types in chronological or geographic linear plots, but work a little differently.
Triggered encounters happen when the trigger is pulled: when the stars are right, when the red lantern hangs from the attic window, when a horned man comes to town, when the murder weapon is found, or when the party goes to ask for help from the seven-eyed wizard. The triggers can be anything, but in a linear adventure, they set each other off like dominos. To meet the horned man, you need the stars and the lantern first.
In a matrix adventure, the order doesn't matter -- and that makes design much more complex. The number of what-ifs is tougher: if the stars aren't aligned yet, does the horned man know when they will be aligned? But if the stars are already aligned, that's unneeded information. The number of permutations quickly grows, which is why I recommend that a matrix plot have just three major triggers, and that everything else be a standard linear element. Go for four major triggers if you feel ambitious, but realize that each trigger is a little like a separate act in a play; it should change the player's goals, or their understanding of the situation in some way.
Once you know what those three elements are, you can design around all the major permutations. Typical triggers are clues (finding a map, meeting the ghost of a dead twin, or deciphering a runestone), time triggers (chimes at midnight, the arrival of a courier), and significant actions (reforging a sword, visiting an oracle). For each of those triggers, I like to have a separate finale scene in mind (see below), but that's probably not necessary. Just make sure that the villain or final battle can take place at any of the trigger locations.
If you want to, you can think of site-based encounters as plot elements are triggered by location, but that underestimates their importance in game design. Location is EVERYTHING in dungeon adventures, because the map constrains the sequence that players can approach things. To reach the big bad evil guy's ultimate lair, the party must walk the road. This is why site-based encounters and linear plots so often go hand-in-hand: location determines the order of scenes, the progression of the plot, the unraveling of clues. But sites can also be a useful way of organizing your matrix plot; the party often visits places on the map until they run out of ideas. Having a map is a way of keeping the party looking around, even if the ultimate encounter isn't even on the jungle map at all, but hidden deep in a cenote, a sinkhole and sacrificial well deep below the jungle floor.
Simply by making the map of sites go through certain choke points, your design guarantees that the party does what you want --- but in matrix adventures, the locations are each a small part of a larger mosaic. In a perfect matrix design, there's enough little bits of the larger picture scattered around that, for instance, after getting any 5 out of the 8 major encounters, a group of players will have enough information to see the finale coming.
The three most important scenes in any adventure are the inciting incident (which gamers call the hook), reversals, and finale. The reversal is usually the point at which a trigger changes the party goals, and the finale is simply that moment when the party finally, finally gets to take down the Big Bad. Structuring a finale, though, is tricky.
D&D design at Wizards of the Coast usually assumes that the final encounter has an EL of at least the average party level plus 2, and often as much as average party level plus 4. The trick to balancing this crucial combat, though, is that it's hard to know just how beat up the party will be at the start of it. Overdo it, and it's a total party kill. Make it too easy, and the party walks all over the encounter that should challenge them the most.
This is why minions, summoned monsters, and henchman can be so valuable to designing a finale: they're a catchup factor that lets you dial in the difficulty. If the party is very hurt, they may just fight some of the villain's underlings and retreat, and the finale itself is saved for a second fight (if the party can find the villain again). If the DM is generous, a party that kills the villain demoralizes all the henchmen, and the fight is effectively over -- the minions flee.
If the party is very strong at the end of the adventure, the minions and other secondary creatures keep coming, keep fighting, and bring in more and more reinforcements -- until at last the party takes down their major opponent, and the night ends as a big success. As a designer, you should consider designing the final encounter with a variable number of underlings to make it as tough as it can be, without going over.
Know what kind of design you want at the start, and build to suit: a straight line, a matrix, or a little of each. Either way, the plot should point to a single finale that can be modified on the fly for maximum entertainment at the Big Finish.
About the Author
Wolfgang Baur is the author of dozens of adventures, from the "Kingdom of the Ghouls" and "Gathering of Winds" in Dungeon magazine to upcoming releases from Wizards of the Coast. He offers custom-tailored adventures and professional advice to patrons of the Open Design blog.