Hawkswick Hall has been transformed into a psychiatric hospital for soldiers shell-shocked during World War One. When local livestock and family pets are found violently mutilated, witness accounts point to horrifically wounded soldiers. The Doctor heads to the hospital to investigate -- two of the inmates have mysteriously disappeared -- and is told by one of the patients that there is an evil presence in the Hall. The key to the mystery lies in that eerie basement room in Hawkswick Hall.