It was all over much too quickly.
Despite his best efforts, Jordan couldn't do anything to save Will Grimes, and he was pronounced dead later in the day. The effects of a severe stroke. Of course, Izzy hadn't been the one to pull the trigger on the spray hose. She hadn't intended to cause his death. That had never been the intention, no matter what kind of scumbag he was.
She felt guilty all the same.
The drive to the hospital had been one of the worst of her life, and she'd been the bearer of bad news enough times before. Telling distraught parents that their child had been killed in a hit and run, or that granny had been found dead in her bed on a welfare check. She was used to that sort of thing. This was nothing of the sort. Jordan had unofficially diagnosed her with emotional shock, but she'd refused any sort of treatment. What could anyone do for something like that anyway? She'd waited in the hospital for news, any news, of what might have happened to Grimes, and even though she'd despised everything the man stood for... when the doctors told Izzy of his fate, she had barely been able to register it.
There were no tears. Not then. She'd simply been numb, a delayed reaction that deep in her mind she knew would come back to bite her sooner or later, but for that moment she had simply stared and nodded as the doctors explained. If she hadn't knocked the spray out of his hands, then he would still be alive. The others tried to reassure her that if she hadn't, any one of them could be dead instead. Or Barry. But it made no difference.
Izzy made her way home alone that day. She refused the offer of a lift in the group's transport, back to the Folly, or to her place on Seven Sisters Road. She simply got out of the car as soon as they were close enough to an Underground station, and rode the train in silence, thinking back on those final moments. Eventually the somewhat circuitous route ended with her stepping off the Tube at Finsbury Park, making her way down the street on auto-pilot. She didn't even remember taking her key out and unlocking the front door as she walked up the stairs to her apartment where Alice and Freya were waiting.
“Hey Izz, how was work...”
Alice called out in a cheery voice as she looked up from her Netflix documentary to see Izzy entering. Her lectures had finished early for the day, no coursework to worry about, and so she had been enjoying a rare evening off, but her voice trailed off as she saw the expression on Izzy's face when she walked through the door. She didn't need to say anything else. Alice got to her feet, moving the cat out of the way as she made her way straight over to the young detective, and simply scooped Izzy into her arms in a tight hug.
“Oh, baby, what's wrong... rough day?”
Izzy had no words. She accepted the hug, and put her own arms around Alice, as she buried her head in the messy chestnut hair of her love, and the emotions that had been building up all day finally spilled out in a flood of tears, deep and heavy sobs as her entire body shook in Alice's arms. They simply stood there like that, for as long as they needed to.
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(post script)
Alice is there for Izzy for as long as she needs her to be. The trust and the emotional strength that Alice provides only strengthens their relationship, and before long Izzy asks Alice to move in with her officially, considering that they've been unofficially living together for a while now anyway. It takes a long while for Izzy to stop waking up in the middle of the night with nightmares from having inadvertently killed a man, but Alice is there to comfort her every time.
The biggest worry is for her job. She considers handing in her resignation to DCI Nightingale, but DC Peter Grant talks her out of it. If any consequences are to come for her actions, then it will be down to Nightingale to decide on any course of action, not for her to offer it. As Peter says, regardless of the outcome, she had been acting to save lives. What happened to Grimes wasn't her fault.
Izzy nevertheless begins a series of counselling sessions to try and work through her delayed trauma and PTSD. It takes a long time, but the long term outlook seems positive. With her colleagues, girlfriend, and family supporting her, things do start to look somewhat better.