In a short blunt summary, first strophe is about a patient in a psychic ward that get's a doll from his/her nurse.

second strophe is about the nurse having intercourse (not clear for me if that's the right meaning) at night in the room next to the patient.

The first refrain is about how, at night, the "doll" will be destroyed violently by the patient. The patient doesnt feel well.

Third strophe tells us the patient sees the nurse killed through a keyhole. Windows are tainted red (sunrise at morning and/or tainted by blood), "somebody" killed her.

Second refrain, the patient now sing he is currently in the act of destorying the doll. The patient now feels very well.