Shortly after Mrs McCarthy refuses to 'help' terminal nursing hospice patient Freda Knight shorten dying pains with a pillow, she dies in bed, but father Brown smells rubber and disinfectant, just like gas mask. Matron Sophia nor Inspector Mallory take his theory seriously, until her estranged son Seth Knight, who pointed at her new heir, sculptor Charlie Coulter, is found died from similar causes, autopsy shows for neither a plausible alternative. While McCarthy fears being replaced by former nun Caitlin O'Casey, Bunty who wickedly planted this paranoia enjoys coming along on account of her hedonistic former nanny Ellen Jennings, who may be next for the angel of death who leaves white feathers behind.
—KGF Vissers