Talk to Daylia the Vigil, who is on the balcony of the Elddar Tree. You are to discover the plot in the Down Below.
Speak to Gelerth, who is back at the archery area. He warns that this is a trap, and is going to turn himself into Rysian.
Enter the Down Below (there's an entrance at 519, -17, -399 in Elddar Grove).
The Secret Meeting is behind a door at -13, 7, 0 . You might want to Stealth before you enter.
You're to stealth to the meeting and listen in. If you're seen you'll be ported back to the door.
A highwayman meeting guard can see through stealth. Don't get too close to him or he will see you.
When you run into the middle of the group of fivehighwaymen conspirators, they'll spring their trap and attack you. Kill them all, then kill the guard and the pair of highwaymen to get your kill count of 8.
NOTE On Test if you died and zoned out the mobs would bug, and be unattackable. If this happens you'll have to delete the quest and start over. Just don't zone out.
Return to Daylia.
Track the "hired assassin" using your tracking and stealth skills North Qeynos.
He's on top of a chain over the bridge ( 416.36, -12.25, -24.52 ) . You must be stealthed to see him.
Knock down the assassin using your range weapon.
NOTE the assassin is a tough fight. You can take him to the guards for assistance.