Go into the basement, turn left, go into the room that leads to the fridge. Face the lockers, go to them and you'll open the path to the rat cave. Search for the ratsuit, change into the Ratticator and beat them bad guys up.
You should now about the rat cave, either because you asked for permission to build it or because Tristan showed it to you.
There's a pattern how to attack them (works for robots and this other gang, too).
Tap the mask-symbol get close to one of the meanies as soon as the first icon flashes green, tap it if he's stunned, the second icon will flash, tap it if done right, the third symbol will flash, tap it
If done right, the guy will be captured. Repeat this with all of the guys. If you are lucky you can catch two at once, but for the beginning it's easier to catch one after another. Be careful, if they face you before you are ready to attack, well. You know what happens.
--- I may be odd, but I always get even. "Gravitation can not be held responsible for people falling in Love" Einstein