No matter how secure its victims think they are, by spending 1 Willpower the creature may suddenly appear in the scene. Perhaps it can manifest out of higher-dimensional space via any right angle, emerge from any reflective surface, or it can simply burst through the wall. Any character wit- nessing this entrance must succeed on a reflexive Resolve + Composure roll or gain the Shaken Condition.
If the characters have actively taken appropriate measures to keep the Horror out (barring and locking the door, smash- ing all the mirrors they can find, etc.) it will take the creature one full turn to break through, giving the characters time to react. If not, it’s just there as a reflexive action and can take one more action before anyone can react.