Just making a guess, but the main arc of a twelve month long story could be Harry trying to find Justine, and deciding what to do with her, if and when he finds her. Plus, because of the recent WoJ that mortals can't be locked up indefinitely in Demonreach, the situation with Thomas will come to a head. However, the emotional core of the story would be Harry working through his grief, finally learning to deal with his anger and other personal issues. Near the end of the novel, perhaps we would see a new Harry start to emerge. One who is a bit more emotionally mature and someone who is finally willing to start facing issues he's long avoided.
Each chapter; or actually each month as one month could take up several chapters, could have Harry dealing with different problems. One month could involve something as simple as a series of public appearances by the Winter Knight in the company of Lara Raith and the fallout that generates. In old romantic and screwball comedies of the 1930's and 40's, often a rich socialite character would have her name in the society or gossip section of a newspaper saying she was dating or engaged to someone and there would often be scenes in a nightclub or on an ocean liner. I'm not sure how this would work in the Chicago supernatural world, but I could see Harry with Lara at some kind of public function, maybe at Arctis Tor, maybe at Club Zero, with a bunch of members of different supernatural nations invited for some special occasion, just to make a public show that Winter and the White Court are now allies. Then Harry would hear from Ebenezer or someone else from the Council, plus who knows how his friends will react. An alternative is that there are several such public appearances that occur throughout the novel leading up to an engagement party, at which point all hell will break loose.
My only other guess is at some point during the year Harry will go to visit River Shoulders and learn from him.
