Sabotage at the City Walls

 An investigation wedged between two combats, suitable for a location a wall to keep the bad guys out.

(Tomasz Zielonka)

The Wall: A BOOM shatters the gentle noise of commerce and smoke rises from a section of the city wall...

• The party could hear (or even see) an explosion coming from the wall (good for adventurers)
• The party could be ordered to help contain the breach (good for military/law enforcement types)

Meanwhile a chunk of the wall has been blown open, allowing a waiting raiding party to rush through the breach.  Any guards present are rapidly being overwhelmed - it's up to the party to defeat the raid.

The raiders will obviously vary depending on what setting you are using.  I would use mainly melee (or at least close ranged) enemies for that "barbaric horde" vibe as they swarm towards the players - this will also give the players a bit of time to strategies and thin the enemies out a bit.

• The Big guy: Could be anything from a troll to a demon or an armored vehicle, but it acts as the heart of the raid.  Once killed, the rest of the raiders retreat.
• The Specialist:  There's always someone that wants to climb up a building, isn't there?  While most of the enemies should favor close in tactics, this one has a long ranged weapon and hangs back and provides fire support.  Could be a sniper, a damage-focused spellcaster or someone with a support weapon.
• The Swarm: A large number of weak, poorly armed and armored close-range attackers.  These guys should bulk out the attack and let the players feel powerful as they mow them down... but can also absorb attacks meant for the big guy.  Consider using minion rules if your system has them, but otherwise pick weak enemies (goblins, thugs, drones etc.) If you are worried about having too many or too little, you can always start with a few and add more each round as they run through the breached wall!

Investigating the Explosion: Once the raid is driven back, the players can investigate the breach for clues.  What they should end up with is that someone in a guard uniform spent a fair amount of time setting up the bomb before staggering away, shortly before the explosion.

• A relevant skill check could reveal that a timed bomb (either alchemical, magical or technological, depending on your setting) was used - and that the bomb maker knew what they were doing.
• A survival or tracking test could reveal that the bomber stayed near the bomb for a while to arm it - asking locals further down the street could get a description.  They might also be able to tell that the bomber was walking poorly.
• If players have access to divination magic, the ability to talk to animals (or if they are available, security cameras) they could get a poor quality image or retelling of the events.
• If all else fails, the players can find a witness - perhaps an elderly person who spends most of the time staring out of their lace-curtained window and is overwhelmingly eager to gossip if the party shows up.

If the players are not under orders to investigate, an official should offer the party a reward if they help deal with the culprits!

Investigating the Guard: If the party head to the local barracks (police station, etc.) they'll need to be diplomatic - they might close ranks if they think one of them is being investigated. The party could...

• Find an excuse to ask about or look for a guard who's walking badly
• Try and find out what guards would be on patrol in that area before the bomb went off and see if any match the description
• The party could use the fact that several guards were killed to turn the guards against their "comrade"
• If all else fails, someone living near the barracks will recognize and be able to name a guard with a bad walk

However they go about it, they should get the identity of the guard-turned-bomber.  They were injured quite badly a while ago (hence the limp) and turned to drink and drugs to dull the pain - something the other guards have been turning a blind eye to.  Note: If your players have had substance abuse issues, it might be better to change the drink and drugs to expensive physiotherapy or a setting equivalent, coupled with a loan shark.  The end result is that the guard is dependent on something and is running out of money to get it.

Unfortunately, the guard's gone AWOL.  The party can get his home address by offering to check he's alright.

The Guard's Home: The guard lives in mediocre conditions (i.e. a rundown apartment or cramped terraced housing.)  The party can knock on his (flimsy) door - but if they do, they will not get a response.  Instead, perceptive party members might hear wheezing, gurgling or odd noises coming from inside.  The door can be broken down with an appropriate test (athletics, strength, unarmed etc.) or picked.

Inside, the guard is semi-conscious and seems to be dying from a slow poison - it seems someone didn't want them to talk.  A medical check or magic could potentially stabilize him - it that (or necromancy) happens, he can be questioned. The idea here is that the ones who supplied the bomb are covering their tracks - they may even have put a contact poison on the bomb itself!

Though his recollections are muddled and hazy as a result of the poison, he will explain that he couldn't pay the gang acting as his drug supplier/loan shark, so they forced him to plant a package on the wall as an alternative.  He can provide directions to where their hideout is.

The rest of his apartment is pretty bare - anything of value has been pawned for money and there's no sign of any bomb-making equipment, backing up his story of being given the bomb.

There are also some bits of paper (either wrappings for a substance or a loan shark "contract") with identifiable gang markings on them - a streetwise character, criminal contact or a guard can point the party towards their territory.

The Hideout: If the party don't have great directions, they might need to make some tests (tracking, streetwise, investigate etc.) to find the hideout.

The hideout should vary depending on your setting, but could be anything from a warehouse to a junkyard or an abandoned building.  The gang are also on high alert - stealthy attempts to get in should be difficult.

The gang itself has more sinister motives than making a quick buck.  Depending on your setting, they could be cultists, rebels, a group of psychopaths or something stranger.  Whatever their higher motives, they want to see the city suffer - and blowing a hole in the wall was only the start.

The gang should contain a mixture ranged and melee enemies - I'd suggest around a 50/50 split.  They should also be things that could blend in with the local population.  For example, for a fantasy majority human city you might consider using a group of bandits (archers and swordsmen) and a spellcaster/alchemist.  In a cyberpunk setting, a weapons expert with explosive weaponry, some riflemen and some pistol or shotgun users.