The summonses go out on the backs of rats which have been pressed into service -- a sort of "message + meal" system which everyone is very happy about (except, of course, for the rats). It is from Teh Grand Purr-bah, and consists of five words: "Operation Catnip Dynamite begins meow."
You handsome kittehs reach Teh Grand Purr-bah's office in record time, where His Grand Felinage is reclining on soft, sumptuous cushion top the desk. His familiar, looking quite wizardly in its black robes, stares vacantly at the door and scratches Teh Purr-bah's ears.
The fluffy white cat perks up when you arrive, and fixes you with a brilliant sapphire stare. "Agents, identify yourselves and report!" he yowls.