If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Sneak and grapplehook through buildings as you shoot out lights, choke and shoot enemies.
WASD/Arrow keys to Move / Swing.
Mouse to Aim and Shoot.
1 - Select Gun.
2 - Select Grapple.
E/Ctrl to switch as well.
Space bar - open doors/ perform silent kill/ skip text.