Nobody saw anything

You are standing on a metro platform full of passengers. Your two little daughters will be the first to jump on the train in a second of your inattention. You rush after them and just then the doors close and the train leaves. And you will be left standing helplessly on the platform. You convince yourself that everything will turn out well. Just go to the next stop and you will surely find them alive and well. But when you arrive, there are not two children waiting for you, but only one. And nobody saw anything. Is it possible that your other daughter is still on the train or is she lost somewhere? Was she abducted by a stranger, a random passerby? Or is the perpetrator closer than you think? No one seems to be telling the truth, and the longer the search goes on, the harder it will be to find your daughter. Time is your enemy and so is fear.