His helping of Dijkstra and the Temerian Resistance plot the assassination of Radovid comes down to the fact that Radovid's anti-magic campaign threatens Yennefer and Triss, people Geralt cares for immensely as Dijkstra flatly points out when laying out his plans.
To make matters worse, I'm sent off to jail, and Geralt weasels his way out with some thrifty Axii skill.
A gravedigger named Silas also accept Parvati as a companion, or solo.
Note: If you attempt to enter the camp, you'll turn all of the slavers hostile immediately, even if you chose the peaceful option during the conversation.