The greeting used by the mendicant is one you know well. To speak of the coming rain is a secret reference used by your brothers and sisters in the low church to identify one another when in the presence of outsiders. This man, like you, is a follower of The Way. To risk exposure, with the Lord Marshall's adjutant nearby, it must be of dire importance. It is not too difficult to break free of Quintus and find out what the mendicant needs.