Amadan na Briona

This is an action-packed alt-history thriller that plunges through an increasingly divergent World War II with two small bands of characters, one British and one German. The British have warlocks who summon demons to fight Nazis who are guided by an oracle who can see the future, and the situation grows increasingly grim for both sides. It's an exciting page-turner, and the supernatural/super-science elements remain just this side of believable. However, Tregellis's plotting is better than his character development. There's fairly little focus on any particular character, so while we get to know them, we don't really become invested in any of them. Also, this is the start of a series, so the ending is, rather predictably, something of a cliffhanger.