Grumm sends Broodwing and a force of Krybots to raid a military installation for their fuel supplies and munitions, and S.P.D. responds to the situation. However, suddenly five military vehicles transform into humanoid robots - its the Combaticons. They engage Grumm's forces, grumbling about their mission being compromised. The Rangers arrive and are confused by the presence of the Combaticons, and the Protectobots soon come in. The Combaticons retreated, but Broodwing tells Grumm they were giving off an unusually high energy reading, a power like he's never seen, and Grumm tells him to follow him. The Rangers and Protectobots are called back to base.

At S.P.D. HQ, Kruger contacts Optimus Prime on Cybertron. S.P.D. and the Transformers know about each other, but these days the Transformers stick to Cybertron, which is outside their jurisdiction. Optimus says he went the Protectobots to track the Combaticons on Earth, and questions why he hasn't heard from them in weeks. The Protectobots explain that the Combaticons have been acting unusually stealthy, scoping out human military installations and sticking to their alt modes, so they didn't want to report back until they knew what was going on. Kruger agrees to help them if they need it. Meanwhile the Combaticons contact Megatron and tell him that infiltration has failed, so they'll need to risk an open attack, when Broodwing reveals himself and establishes a call to Grumm. The two tyrants chat and Grumm learns that the mission the Combaticons were on was to steal a top-secret weapon the humans are developing, and the energy source Broodwing detected was energon. Grumm says he can deal with the Protectobots, and the two agree to a temporary alliance - the Empire will help the Combaticons steal the weapon in return for Megatron giving Grumm a cache of energon.

S.P.D. and the Protectobots are alerted to another attack from the Combaticons and they head out to deal with it. The Rangers immediately go to call for their zords, but stop when they see Krybots and one of Grumm's monsters on the ground, confirming the two enemies are allied. The Combaticons engage the Protectobots a bit and are pretty banged up, and they call to combine into Bruticus. The Protectobots combine into Defensor, but this is the cue Grumm's monster was waiting for. He blasts Defensor with an energy beam that causes it to destabilize and fall apart, the Protectobots going back into their alt modes. The Rangers have mopped up the Krybots and they call in the Delta Runners, and they're able to chase off the Combaticons.

As HQ the Protectobots are revealed to have been hit with some sort of disruptor array that has damaged their transformation circuits, trapping them in their alt modes. S.P.D. can repair it, but it'll take time since Cybertronian technology is so advanced. With the Protectobots out of the picture, Grumm's forces and the Combaticons raid the military base again. The Rangers head out to confront them and form the S.P.D. Delta Megazord; Grumm's monster tries to disable it but fails, since its weapons was made specifically to disrupt Transformers. The Megazord does decently against the Combaticons, but then they combine into Bruticus and severely damage the Megazord. The Rangers are forced to withdraw, and Bruticus gets its hands on the new weapon - a massive laser cannon artillery piece that just so happens to fit in its hands as a weapon. Seeing this, Megatron naturally wants it for himself, and Grumm is also thinking that the Combaticons are so effective that they may be more valuable to him than mere energon.

The Combaticons begin to set up the laser artillery with intent to use it to blow up Delta Base and wipe out S.P.D. and the Protectobots. With their other zords unable to take on Bruticus, S.P.D. has no choice but to deploy the Delta Command Megazord, while Sam pilots the Omegamax Cycle alongside the Protectobots, who want to try and help even trapped in their alt modes. The Delta Command Megazord and Bruticus collide and the Megazord does well, but as Sam destroys Grumm's monster, it uses its powers to made Bruticus grow ever *bigger*.

Bruticus brutally overpowers the Delta Command Megazord. Bruticus prepares to use the laser battery to destroy them, but then Kat and Boom tell Kruger they have an idea - the Protectobots can't transform because they aren't fully repaired yet, but that's primarily because their processors are unable to do it, they could *physically* transform if they had the capacity to control it. With this, the Protectobots interface with the Delta Command Megazord's systems, allowing the Rangers to pilot them remotely, and the five Autobots combine with them to form the Delta Defense Ultrazord, which uses the SWAT Flyer Cannon to blast apart the overgrown Bruticus and make it shrink.

Grumm and Megatron rage at each other, naturally, and refuse to work together ever again, and Megatron recalls the Combaticons to Cybertron. The Protectobots are fully repaired and go home as well, agreeing to come lend S.P.D. a hand if the Decepticons return again.