Tigana is a novel about identity, and freedom, and the effect it has on people when you take away their identity and their freedom.
The Palm is a peninsula, in which the provinces have been occupied by two sorcerors, who butt heads along the fence line. In revenge for the killing of his son in battle, one of the sorcerors has utterly destroyed the province of Tigana, and enchanted anyone not born in the province, so that they are unable even to hear its name. As his enchantment dies with him, his intention is to live until the last person born in Tigana is dead, and the country is totally forgotten.
In order to restore their name, and their sense of identity, a group set out to kill him -- but it isn't that simple. If they don't overthrow both tyrants, they will simply replace one overlord with another.
There are several subtexts running alongside the main theme. A tragic love story, the need for unity amongst old enemies to overcome a greater evil, the way obsession can blind people to what is going on under their noses, what must be sacrificed to achieve an ultimate goal.
The characters are beautifully drawn, however small a part they play. The motivations of both sides are shown, and nobody is all hero or all villain. The writing is exquisite and the plotting completely involving.
Kay manages to draw the reader in completely, you can't help feeling for the characters, and I've never met anyone who has read the book without crying.
If you only ever read one fantasy novel, this should be it.