Tristan shakes his head. "I'll help you, I swear it, but not with them - at least not [i]tonight[/i]. They were kind and generous to me, and to turn on them without provocation? Dishonesty has been hard on me enough without outright betrayal. I would not have you know me as someone so fickle with the trust given to me. Besides," he races to add faster than Robena can interrupt, "Her quest is likely a doomed one, a reckless reading of prophecy. One of Merlin's."

Tristan is still convinced that Merlin is unimpeachable, a conviction like bedrock. Either the prophecy is a trap for Pellinore, or her accomplishing it is for the common good, no matter her personal allegiance and culpability. In either case, it's a waste of risk and resource.