On Halloween night all angels have their hands full, and this night is no different for Monica, Tess, and Andrew, who attend to a spiritual battle at Salt Lake City’s Mercy Hospital. The ambulance brings in Lonnie, a deranged and suicidal homeless man. Lonnie frequently visits the ER and Duncan, the head of the ER and Lonnie’s best friend from childhood, has diagnosed him with Multiple Personality Disorder.

Andrew arrives to comfort Lonnie, but suddenly lucid, Lonnie claims to be “Gregory” and recognizes Andrew as an angel! Andrew looks to Tess for some insight and she relates Lonnie’s history: Many years ago, when Tess was Lonnie and Duncan’s Sunday School Teacher, she taught them that faith in God is like a mustard seed — though little, it can grow to be very large. Despite an abusive home life, Lonnie struggled to have faith, and cherished the mustard seed that Tess gave him. One Halloween though, a prank gone awry resulted in Lonnie burning a house down. Monica then continues the history: Lonnie’s guilt and shame over this event initiated a downward spiral that ultimately resulted in Lonnie becoming involved in drugs and, then, the occult. When “Gregory” claims to have power over Lonnie’s soul, Andrew finally understands — Lonnie is possessed by a demon! “Gregory” claims that Lonnie’s soul is fading and that he will soon be completely possessed.

In a moment of clarity Lonnie calls out to Duncan for help, and clutches something in his fist. It is the mustard seed he has kept since childhood. But when an orderly accidentally crushes the seed, Lonnie gives a final cry and “Gregory” says he has full possession. Tess appeals to Duncan to help his old friend, telling him about Lonnie’s spiritual condition. They corner “Gregory” in the boiler room where he is waiting for Lonnie’s body to die. Rather than give up hope for Lonnie, Monica pleads with him to ask God for help. “Gregory” howls in pain. Duncan, frightened, runs from the room. Tess follows him and reveals herself to be an angel, and tells him that Lonnie needs his help now; he needs someone to stand beside him who has a strong faith.

In his office, Duncan finds his old mustard seed and returns to the boiler room, telling Lonnie that the seed is only a symbol of faith, real faith comes from the heart. Duncan’s presence gives Lonnie the strength to cry out to God, asking for forgiveness and help. “Gregory” screams in pain, finally defeated. Redeemed, Lonnie wonders at the realization that, through it all, God never gave up on him.