Brimming with excitement and hope for a fresh start, Josh and Renai Lambert move into their new home with their three children. But the couple's bliss is short-lived. As a mysterious accident leaves their boy, Dalton, in a science-defying coma for months, blood-chilling occurrences in the house can only mean one thing: something evil has set its sights on robbing the Lamberts of what they hold dear. With sickness replacing happiness, experienced paranormal investigator Elise Rainier agrees to infiltrate The Further, the dark realm of lost spirits, to search for the Lamberts' missing son. However, after the life-altering experience in Insidious: The Last Key (2018), Elise is more exposed to all-consuming darkness. As answers demand courage and faith, could Dalton's shackled soul be trapped behind the ominous red-lacquered door?