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Isabelle thought nothing of it the first time it happened.
Everyone’s stress level was through the roof, and the last thing she was paying attention to was Alec doing something as simple as checking the perimeter. He did it all the time, mostly because if her and Jace were ever caught off guard he could come in from behind and fend off whatever they were facing with his bow and arrows. It was a simple tactic, one that they learned early on in their training.
Sure, she was a little bit surprised to see that both Alec and Magnus had been caught, but Valentine’s lackeys were not exactly the easiest to beat, and they were all exhausted. They had absolutely no time to rest before they had to get to the bottom of Hodge’s betrayal and find the Book of the White, and everybody was on edge. Not to mention it was likely that Alec was distracted by Camille’s speech about aging. Him and Magnus had just begun to figure things out, and that certainly wasn’t helping matters.
But as time went on, she started to notice it more and more, how Alec would offer to do it whenever Magnus accompanied them on missions or when he arrived just a little bit late to meetings, claiming, “You can never be too careful.” He had gotten very good at being casual about it, playing it off like it was nothing, and of course no one questioned him. He was the Head of the Institute, and while some were not happy about that fact, they didn’t often voice their opinions out loud for fear of being punished.
It was the tiniest flaw in his otherwise impeccable organizational skills, and Isabelle’s curiosity got the better of her, so she decided to investigate. She had to wait a few weeks for Magnus to join them on a mission again, but it eventually came to fruition. It always did with those two. They were attached at the hip whenever possible, like two powerful magnets that took a lot of force to separate. Just like every other time, Alec offered to check the perimeter almost as soon as they got to the location, and Isabelle agreed with an easy smile. Jace and Clary were as oblivious as always, wrapped up in their own little world of annoying PDA, so Isabelle had no problem slipping away just a moment later, following behind her brother and Magnus with ease.
At first, she thought that Magnus had portalled them away when she suddenly lost sight of the two, but then she spotted them right as they ducked into in a little indent in the building and huddled together. Alec’s back was against the wall, Magnus’ hands resting on his chest, and something warm settled in Isabelle’s heart. Magnus was laughing quietly, leaning forward to press his grin into Alec’s neck, and the smile that spread across her brother’s face was the most genuine she had ever seen. She had witnessed it before, the dopey grins and the heart eyes, but that was always in public. They were different like this, more relaxed.
The second that realization hit her, she backed away silently, not wanting to snoop any longer than she already had. Her brother deserved this, to be able to mix work with pleasure every once in a while, to be just a little bit selfish. She was going to tease him just a little bit once someone else figured it out, but she decided she would keep her mouth shut for the time being. It was his life, his love, and she would never want to make him feel guilty for that.
They returned to the group no more than five minutes later, and to anyone else they would have appeared completely innocent with their serious expressions and tense postures. But as they moved toward the building that they were going to infiltrate, Isabelle heard the small huffs of laughter that escaped both of them, and she smiled.
It was music to her ears.