From the introduction:

Floods, earthquakes, giant robots, atomic doppelgangers and an alien invasion: the heroes are in for a busy day.

This adventure is a sequel to Day of Dr Null and Dr Null: Battle on the Bay Bridge (a free download from Lame Mage Productions), but it can be used without either of those scenarios if you prefer.
In Dr Null: Battle on the Bay Bridge, Dr Null unleashed a horde of mechanical insects, robots programmed to construct more and more replicas of themselves from raw materials they scavenged from their surroundings. His plan: world domination through recycling.

In Day of Dr Null, he hatched a scheme to transfer his mind into the body of the Neutron Fist, an unstoppable criminal powerhouse cursed with a disintegrating touch that prevents him from ever leading a normal life. This was merely a prelude to his real plan: to conquer the city with an army of Atomic Supermen, mass produced synthetic clones with inhuman strength and radiation powers, and conditioned with absolutely loyalty to their creator, Dr Null.

In the first part of this scenario (Open House) the heroes track Dr Null back to his secret base, braving the mad scientist in his lair to bring him to justice and end his reign of terror. The heroes have to endure cunning booby traps and then defeat the monstrous creations of Dr Null’s labs… only to discover that they are too late, Dr Null has already departed to inflict one more fiendish plan upon humanity.
In the second part of this scenario (Dam Dr Null!) the heroes follow Dr Null to the Blake River Dam, where he seems prepared to destroy the dam and flood the city in a final act of spite. His real plan is far more diabolical–he intends to use the electricity from the dam to power his Seismic Converter, a device capable of inducing earthquakes across the globe.

As described in the Origin of Dr Null, the Seismic Converter is the same invention that caused the accident resulting in Dr Victor Marsden’s amnesia and his rebirth as the nefarious Dr Null. Events in his life have come full circle–the device he once invented to help mankind is now his ultimate weapon to destroy the world he has come to despise.

If you are running Day of Dr Null back-to-back with Death of Dr Null you can have all the action of both adventures packed into one very long day: Dr Null tries to mind swap with the Neutron Fist before noon, the Atomic Supermen attack the city shortly thereafter, then the heroes track down and invade the secret base in the afternoon or evening, with Dr Null taking over the dam that night, making it truly one extra-long action-packed day of Dr Null!