Kaz and Oliver are exhausted and stuck working the overnight shift during a lunar eclipse, when it is rumored that the freakiest patients come to the hospital. When Neocortex checks in with an illness that unintentionally traps people in their worst nightmares, Kaz and Oliver desperately try to stay awake and figure out how to save everyone from their nightmares.

Oliver and Skylar pet sit Horace's shark that is kept in the aquatic wing of the hospital. When Oliver feeds the shark the wrong food, the shark evolves into a man-shark.

When superhero Spark, a tough-as-nails teenage girl, meets Kaz at Mighty Med, they have an immediate connection. However, it fizzles quickly when she becomes overly possessive. Meanwhile, Horace puts Skylar in charge of security to keep villains out of Mighty Med.

The Key Keeper announces his retirement, and Skylar and Kaz both express interest in becoming his replacement. Meanwhile, Oliver meets his mother's new boyfriend for the first time.