Phineas and Ferb build a super computer so that they can find the perfect way to do something nice for their mom.

In the meantime, Dr. Doofenshmirtz searches for the key to his All-Purpose-inator, an invention that he believes to be extremely evil despite not knowing what it does.
!!Tropes present:
* CaptainObvious: The super computer. It may have cryptic meanings, but the ending had it be this way.
* NoodleIncident: With the Tri-State area itself. With all the gladiator helmets Doofenshmirtz unearths, you'd expect that there was some sort of war fought there before.