Storm rising - Mercedes Lackey

Nothing is certain for the state of Valdemar or her neighbours,the normal rules no longer apply,for violent and unpredictable changes in the laws of magic have beset them all,enemies and allies alike. Duke Tremane is landlocked in Hardorn,abandoned by his Emperor and with only surly and impatient troops to keep control of a townful of citizens under siege.And in all the lands an early autumn is threatening a terrible winter of hardship-Hardorn looks likely to suffer more than most.Tremane has the key to surviving the onslaught of magical storms,but using that key may endanger his stranded company even more...