This novel is set in Abercrombies "First Law" world some time after the end of the first trilogy. It has a very restricted scope being largely restricted to a single battle between the armies of the Union and northern forces led by Back Dow. The Heroes of the title refers to an ancient hill which forms the centrepiece of the fighting but of course it also refers to the characters who play out the action. The book scored very highly on two fronts: deep characterisation and masterful depiction of battle. We follow the toils and motivations of a motley crew of characters on both sides of the divide. A battle weary "named man" on the Northern side leading a unit of hardened fighters. A disgraced former personal guard of the Union King who fights like a man possessed perhaps in hope of winning his honour back, perhaps because he just loves war. The daughter of the Union commander equally full of contempt for he inept union generals and ambition for herself and her husband. The battle shy younger son of the former Northern ruler that Black Dow displaced. Despite his lack of combat prowess he too has ambition to regain his fathers place.
With regards to the battle scenes that fill most of the book all I can say is that Abercrombie is that I haven't been as engrossed in descriptions of battle since David Gemmel and that is high praise indeed.
The main flaw of the book for me is that it rook too long to finish up. About a quarter of the book is devoted to tying up loose ends after the main plot is already resolved. Perhaps this is a consequence of the deep characterisation with so many individual sub plots to resolve but to my mind it goes on way too long.
And yes the Bayaz the first of the Magi is involved as usual and yes the outcome is just as you would expect.