The Danes blithely wandering into a forest ambush with no clue of the hordes of Saxons lying await on either side of the forest trail; no scouts for the mighty Danes, then, even though the idea was clearly present since the four sent by Brida were caught, sliced, diced and strung up handily athwart the trail?
And then, we're losing, no wait, the Mercians are here, without their detestable ant of a sort-of king.
Also thought it was the plot hammer as much as the spear throw that killed Sigebriht after he decided not to be such a twat and actually fight for his, you know, own kingdom. Big of him, and that's what happens...
I also totally understand BPs admiration for the character Æthelflæd, and more crucially the actress Millie Brady...