Patience is a virtue, Arianna exhibited that as she waited for the perfect time to execute her plan. Marcel must not have noticed the patrol car or he trusted her too much - and that would be his downfall.
Marcel lifted the cuff hesitantly with the gas attendant's attention on them. He knew it would draw attention if he cuffed to the car as she did to him. He might be above the law but not public opinion. If this was caught on camera, it would pose a problem for him.
So he used his wits instead.
Marcel leaned towards Arianna and in the gas attendant's view, it looked like they were young lovers making out in that position. However, he simply whispered to Arianna's ears, "Don't provoke me, love. Stay still and don't cause trouble because your saving grace is almost up,"
Arianna didn't give him a reply but he was sure his words were well received with the way she turned her face the other way with a scowl. That was good then.
