From the Introduction:
Dr Null: Battle on the Bay Bridge is a prequel to Day of Dr Null, an M&M Second Edition Superlink adventure from Lame Mage Productions. This short scenario is intended to introduce Dr Null to the heroes and set the stage for the later adventure, but it can be played as a stand-alone game even if you do not run Day of Dr Null.
If you are running Zodiac Ring you can insert this scenario in the middle as an unexpected break from hunting down Zodiac avatars.
Dr Null: Battle on the Bay Bridge is an excellent simple scenario for a night of gaming if you want to try out M&M Second Edition or introduce new players to the game. The scenario also provides details for running a battle on a suspension bridge, so you can use this information in other games set in a similar environment.