Kill Kagha is a sub-quest of the Druid Grove's main quest Save the Refugees. It can be initiated by talking to Zevlor after Kagha sends the party to assist him in getting the tieflings to safety.
The quest to kill Kagha can be received after speaking with Zevlor once Kagha requests the party assist the tieflings in moving on. The party can ask Zevlor "Can you delay the ritual?" and he explains that it is Kagha's influence that is causing the intolerance to outsiders. Selecting "Then why don't you get rid of her?" has Zevlor agreeing, but stating that the tieflings cannot enter the Inner Sanctum, while the party can. The party can either take him up on the offer or decline.
After this conversation, Kagha can be killed at any time. However, if Kagha is attacked unprovoked, a cutscene starts in which a signal is given and the druids commence a pre-arranged slaughter of every tiefling within the Grove. The druids also become hostile to the party with the notable exception of Rath and Silver who side with the tieflings. As the fight happens in real time, careful planning is required to avert a massacre. The final stand takes place in the makeshift prison where all the tiefling civilians are holed up. If enough of them are killed then Save the Refugees fails.
If the party complete Investigate Kagha and find evidence of her collaborating with the Shadow Druids, then Kagha can be confronted without the druids becoming hostile. The party has a chance to sway Kagha to their side, otherwise the party can simply state that she is too far gone and fight her to the death with the other Shadow Druids. If she is slain, Loic and Marcoryl join her. Either choice results in the Rite of Thorns being stopped, and the tieflings are allowed to safely leave the Grove when they are ready.
