A tricky one.
If the rumours don't indicate that Penkus is being held against his will, then the LDs don't really have any reason to attack - as far as they're concerned, the guy was simply killed in an unfortunate accident, and Vanthus is no longer there to tell them differently, having departed for his meeting with the smugglers, so if he turns up miraculously alive, that's a good thing.
Most likely, after a couple of days the LDs will send out a thief or two to infiltrate Vanderboren Manor (or wherever the PCs are claiming Vanthus is) and ask Penkus why he hasn't reported back. If captured alive, the thieves don't know about Vanthus's current operation, and will believe that he is either in the guildhall or out about town on guild business, due back in the guildhall at some point soon. With reasonable persuasion methods, they'll tell the PCs what they know about the guildhall, including providing a sketched map. Give the party an unmarked map of everything except the inner chambers past the training room, and they should soon get the hint that here's a dungeon for them to explore.
If the rumours include a suggestion that Penkus intends to inform the authorities about the LDs' activities, then the group sent to investigate should instead be an assassination squad.
|
I'd probably start with a hit squad. By now, Vanthus has had time to turn everyone away from Penkus, so he might not have as many allies in the guild as he did in life. You could have the urchin's note be an offer to ransom Penkus, and if the PCs don't produce him stat, the hit squad has orders to find out where Penkus is being held so they can kill him. RK is cynical enough to figure that if Penkus hasn't shown up, he's plotting revenge against Vanthus and/or the guild, so he must be eliminated. Penkus knows too much for the guild to allow him to be loose for long.
Edit:
If you really want to force their hands, have the LDs kidnap Lavinia and/or her maid, and offer a prisoner exchange.