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The group files out of the building. With one last glance GG backs out and closes the door. He goes to lock it with his tools, but finds the locking mechanism is empty.

Was this an unmaintained, damaged lock, or an open invitation for danger?

As the group watches GG a small dart lands beside Tornak's feet.

"Tornak, did you take this lock earlier?" asks GG mildly.

Renwick looks around for the source of the dart axe at the ready

The door was unlocked when you approached.

If there's currently no way to lock the door GG shrugs and says, "Unless anyone can figure out how to get a lockless door to lock then we should go."

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Afterthought: with al the various odds and ends the group has found throughout the house would any of those obviously have a lock that could be readily fitted here?

"Yep." Faltbelly agrees, "Before it starts raining darts."

I don't know if you have ever put a deadbolt in a door, but it takes a few screws and a bit of time. You would have definitely found door locks, but whether you want to take the time to install one is up to you.
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Luckily there is only a single dart.
Then a bird call, from something that sounds exotic. Then a flash of a reflective surface, in a window from across the street.
It is clear the mirror holder is reflecting light from the bar next door at and around the dart.

Renwick picks up the dart and looks at it.

"Looks like someone wanted our attention. It worked," Linar says and heads towards the mirror-holder. "As drugs are involved, you might want to decline, or at least not consume, any hospitality."

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My internet is down and data allowance on phone nearly used up. If I go quiet, that's why. Please let Tristan and Jen know).
Edit: Internet connection seems to be fixed, fingers crossed.

"GG Wait." he says uncharacteristically. "It might be more drows or their companions. They didn't shoot us... yet. They may think we are also working one hand with the drows. We need to be extremely careful. If the lords had known about this they would have let us know." Then he wait to see if all are ready to go meet the mirror holder and joins the group.

GG gives Flatbelly a brief smile of thanks, adds, "It'll be fine. You can head off to the house. I've got this." As an afterthough he adds, "Actually you could all stand by the corner of the street over there and I'll scout." With that, he wignles his fingers and disappears.

(GG puts up Invisibility and moves stealthily* on an indirect route towards the mirror-holder**.)

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*With the benefit of Boots of Elvenkind.
**Happy for GM to cover this quickly so that other players aren't waiting for ages, even if it means more or less wasting the spell slot.

As soon as Renwick picks up the Dart he sees this badge: Same as the one on the Token given earlier.

When the dart is picked up, the mirror goes dark and out of sight.

The group sees GG start to slink across the street, and cast a spell.

Tornak shrugs and heads out to the corner of street content to let the elf take point.

Renwick hands it to Adrick, Seems like an invitation. Anyone fer an ale? he asks as he heads for the tavern, covering the head of his new axe

Tornak softly says "Next door to the tavern" as Renwick passes him