By twisting the flow of time into knots, you cause one action of your choice taken within range within the last round to be undone. Reality then reasserts itself, recoiling from the damage caused by removing an event from time. The direct effects of that action, such as damage dealt by an attack or spell, are undone, but the indirect effects, such as creatures choosing to move to different locations, are not. The creature that took the action takes 10d8 psychic damage, as it copes with its history being modified.