When a flying machine crashes, killing a man on the ground, Murdoch's investigation uncovers high-level conspiracy and sabotage in the race to achieve the first human-controlled flight.

When an anonymous madman threatens the citizens of Toronto with a deadly toxic gas, Murdoch must race against the clock to stop him.

Detective Murdoch investigates the sudden death of bicycle racer Joe Fenton. Murdoch was himself a participant in the race trying out his newfangled gear shifting device but Fenton was the favorite having won several recent races. Fenton's manager, Chippy Blackburn, was seen giving him a potion and they suspect he may be may be fixing races. Dr. Grace however is having considerable difficulty finding a cause of death and with Dr. Ogden's assistance performs her first brain bisection. It leads her to believe he suffered a cerebral aneurysm leading to a brain hemorrhage. The discovery of an injection mark in Fenton's right arm leads to a different conclusion however. Meanwhile, Julia prepares to sell Darcy Garland's house but finds that his younger brother Leslie living is living there.

While investigating a mysterious death in Markham, Det. Murdoch discovers a hidden ornate and booby-trapped laden building that could contain the Holy Grail.

During a women's fashion show for undergarments, a model is found dead.

While investigating the murder of a rich benefactor and the theft of children's presents at a Christmas charity pageant, Murdoch discovers suggestions that a Christmas monster, a Krampus, may be involved.

Inspector Brackenreid learns that his youngest son, Bobby, is wanted for murder, while the Murdochs and Crabtree suspect old enemies are returning to harm them.