All the King's Men

You get the quest from Triss Merigold at the beginning of chapter 3 when she hands you a pass. When you exit her house, you will be asked to present your pass. When you are on your way to the New Narakort Inn doing the quest "A posh reception", you see Thaler and Roderick de Wett having an argument. Approach either one of them, and talk. Do not make your conclusion before hearing out the other side. Thaler will point something interesting out, so let him live. You can continue your conversation later on in the New Narakort Inn - see A posh reception. In order to progress this quest, complete the Lock and Key quest - Radovid the Stern will fill you in with further details.

NOTE: I was in the New Narakort Inn meditating BEFORE the "A posh reception" quest, therefore I met Thaler and Roderick de Wett AFTER the posh reception. It did not seem to break the game though.

To be continued...