The adventure starts in a tavern.
Tell the player characters that they're friends and allies. They've been in this village for a while. They're the official adventurers assigned to this village, and their job is to maintain order and generally make sure nothing goes wrong.
They're in a tavern, eating lunch, and people outside are screaming. It's not the good kind of screaming, either. It's not "I just won a hundred gold pieces" screaming or "I'm on a rollercoaster" screaming. It's "I'm probably going to die soon" screaming.
The group runs out of the inn. There's a mob of people outside, which is not unusual for lunchtime. Down at the end of the block, coming from the cross street, next to the wall surrounding the village, there's an elderly human woman wearing a blue dress. She's holding a giant -- what is that -- you guess it's a sword? But it's way too large to be a sword, and if it's really metal then it's got to weigh two or three hundred pounds, and it's made of polished obsidian and also it's covered in blood. "I'm really sorry!" shouts the woman. "Run away! Run away before I kill you! I'm so sorry!"
A guard steps up to the woman and draws his sword. You recognize that guy. He's Guardsman Rhogar. It looks like he's going to kill the woman.
What do you do?
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This adventure starts with a battle. Draw the street. Put a bunch of tourists in the street, streaming away from the battle. Leave a few tourists rubbernecking at the battle, because there's always some.
The street is twenty feet wide, but five feet on either side is taken up with food and drink booths, so there's really only ten feet of usable space. The group is probably going to want to get closer to the action, but there's a crowd of tourists running away from the action, so it will take some effort to get closer. Ranged attacks get disadvantage if shooting past the tourists. If someone asks to climb up on a roof, let them do it with an easy skill check.
Guardsman Rhogar can see the trail of corpses behind Martha, and he's determined to kill her. It's not going to work, because Martha has absorbed the life force of all the people she's killed, and if she takes any damage it heals instantly. Martha doesn't want to kill anyone, but she's powerless to prevent her artifact weapon from killing Rhogar, after which it will start on the tourist rubberneckers (or the player characters)!
The group recognizes Martha when they get close to her -- tell them that this is Martha Butler, the head curator at the Museum. The group also recognizes Guardsman Rhogar. The group count as senior guardsmen, and the village guard will obey their orders.
The group should quickly figure out that they need to disarm or disable Martha. Once they do that, the artifact weapon will be lying on the sand. Rhogar, or a player character, or a tourist, might pick up the weapon, either because they haven't realized what it is, or because it used its mind control power to force them to do that. The group might have to do several rounds of disarming.
In the meantime, if anyone goes down, they're going to stand back up as zombies pretty quickly. Healing them before that can save their life. More zombies will come from the cross street, the one Martha just killed a bunch of people on.
When the artifact weapon is on the ground and everyone is standing back from it, and when the first wave of zombies are dead, advance to Scene 2: What Just Happened?