Rob and Tom were inmates on a Chain Gang until the crooked governor did a deal with an unscruplous laboratory. Injected with an ever-mutating DNA, the two guinea pigs gained the ability to transform into random creatures. It was discovered that while Tom's transformations were completely random, Rob had learned to control his changes.
Every night the two inmates were shackled together by their ankles (with a special indestructable chain and leg-irons that were created to resize to fit them, the same ones that secured them during the experiments) and injected with serum that briefly stopped the transformation process overnight.
One night however, the scientists forgot to give them their nightly injection...