Just after the conversation with Markus, Lucas will have a vision of a kid slipping into the ice – but rescuing him means being recognized by a nearby cop. Run forward and dive into the river to save the kid. Follow the
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QTEs, and when you get the kid out of the water, perform chest compressions on him (you don't need to listen to his chest). It will take four successful compressions to revive him, so if you're almost out of time, quit to the main menu and try again.
Solution taken from PlayStation Trophies:
https://www.playstationtrophies.org/game/indigo-prophecy/tro...