James gives Raju a very flat look in response to the ruse and Raju's raised eyebrows, but there's clear amusement beneath the expression. He's not really about to go along with this--if they're going to be this obvious one of them should've just gone to get Francis--but does find it at least a little funny.

But before he has to come up with a quip, whether directed at Raju or in theatrical response for Francis' benefit, Francis finally reappears. He seems to be less melancholy, which is a relief, although at that look around the room James absolutely has to remark--

"Come now. You cannot possibly have believed that." The lightness in his tone is easy, coming naturally this time instead of being purposefully affected. "The one thing I do know about cooking is how to maintain a fire. There will surely be enough to critique about the rest of my efforts, however, as I have no interest in simply watching preparations being made." Hence being in the kitchen, as he's invited himself to being a part of the actual cooking.

This is definitely what happened, and it is certainly not just a smoothly improvised part of the plan.