As you are, no doubt, already well aware, Geralt has always paid particular interest to crowns and the men who wear them. Kings, you see, are always in need of specialists to perform dirty jobs for them. When Geralt heard King Radovid wanted to see him, he surmised this was just such a moment and set off in the hope a profitable witcher contract was in the offing.
And this time Geralt was not mistaken. Radovid asked him to track down and bring back Philippa Eilhart, a sorceress Radovid hated with a particular fury.
This quest and several others started by it will not trigger at all if you bypass the conversation with Radovid's guards after completing Get Junior by fast traveling out of the compound (possible solution).