The Spider and the Fly - S5.E2

Jane rushes back from New Zealand where she has been lecturing, for the funeral of her best friend, Dr. Lisa Hardman. Staying to help Lisa's husband with the children and to wind up Lisa's psychiatric practice, she discovers a patient who displays a dangerous obsession with Lisa's family. Jane begins to suspect that Lisa's death was not due to natural causes and when first she, then Lisa's husband, get sick, Jane realises that she is dealing with a serial poisoner.