Falconer and the Great Beast — Ian Morson

It is 1268. Oxford is forced to play host to the Tartars, a tribe from the East whose deeds have wreaked havoc in France and Germany. This time they claim their mission is a peaceful one -- they merely wish to gain audience with the king. But are they to be trusted?

When the Tartar ambassador is found dead, it looks like cold-blooded murder. Falconer is on the case once more, but even when he thinks he's solved the case, he still has to trick the murderer into giving himself away.