A young woman dies after she starts bleeding from the eyes, nose, and mouth while at a party aboard a subway train. Mac originally believes she is the victim of a biological attack. Later, it is revealed that Sheldon knew the victim. Across town, a wealthy playboy is found dead in an indoor lap pool in his penthouse suite. The investigation reveals that he was murdered and his last maid was fired two days earlier.

Sheldon Hawkes goes under water to gather clues but could be in danger when he can't come up for air. Mac learns of something else under water.

After a series of heists in the city (one including Det. Chief Sinclair's house) one of the "super spies" involved is robbed of his life. The team works to solve the robberies and the murder, as both are obviously connected.

Mac and his team finally believe they have captured the taxi cab killer but there is one problem - he is found dead. Mac must figure out how to keep the streets of New York City safe while continuing to track the elusive taxicab killer