The "Door of Death" in the title refers to a warning sign on a greenhouse dioor referring to the lethal gas used in the cultivation of orchids. Because his regular gardener has taken a leave of absence and orchid lover Nero Wolfe is desperate to find a replacement, the rotund investigator leaves his brownstone and takes a rare car trip to an estate in Westchester. He is anxious to close the deal with an expert orchidist to become caretaker of his beloved plant room. He is so impressed with the gardener's expertise that misogynistic detective even agrees to house the man's fiancee under his roof as well. Unfortunately they find her under one of the plant tables in the greenhouse dead from poison gas. Suspects include the gardener and the eccentrically dysfunctional family living in the manor house.