The Empire has dispatched a series of probe ships across the galaxy to track down the Rebel's base of operations. One of them arrives on Atollon, and after it lands some kind of protocol droid emerges from it. It takes a few moments to scan its surroundings and then heads out, just as it comes under attack by two Krykna Spiders.
Meanwhile at Chopper Base, the Ghost Crew and Phoenix Squadron are heading out for a training exercise, leaving Zeb in charge of the whole base. However, Zeb is not happy about being left behind. He does not want to get bored or be in the company of Chopper or AP-5. AP-5 is also not so keen about Zeb being left in charge of the base, as he always assumed him to be somewhat of a "grunt". After a brief, but insulting, conversation, AP-5 goes off to conduct a thorough inventory of the base's munition supplies. He offers either Zeb or Chopper to assist him but both of them pass and leave. The two of them arrive at the command center, where they receive reports about meteors impacting on the surface nearby. The Rebel officer making this report suspects that one of them may have knocked out one of the perimeter sensors. He offers to send a unit but Zeb chooses to handle this personally.
Accompanied by Chopper, who came along only because he did not want to help AP-5 with his supply inventory, Zeb arrives at the knocked out perimeter sensor in a speeder. They have brought along a new one to take its place. As they inspect the damage, they find no evidence of a meteor crash but they do find two dead spiders and underneath the droid that was dispatched from the Empire, powerless. Zeb suggests they take it back to base and find out where it came from, but Chopper disagrees and insists they trash it. Zeb does not listen and carries the droid back to the speeder. Word about the droid being out of contact with the Empire is soon reported back to an Imperial fleet, operated by Agent Kallus. The reporting office suggests alerting command to investigate, but Kallus recommends they be patient for now rather than waste time chasing down every temporal comm failure. Back at Chopper Base, Zeb and Chopper present the droid to AP-5 who is still conducting his supply inventory. AP-5 identifies the droid to be a protocol type, and after giving it some power to restart its systems the droid reactivates. Zeb tries to talk to it but the droid does not appear to understand due to having a damaged memory system. Then, to their surprise, the droid scans the entire supply inventory. Both Zeb and AP-5 are impressed that they decide to keep him, making him as AP-5's assistant. Leaving the droid in Chopper and AP-5's care, Zeb is needed at the commander center for a priority message from "Fulcrum". Upon arriving, the Zeb is patched through to "Fulcrum", who warns him about a series infiltration droids being dispatched by the Empire to sweep the Outer Rim worlds for Rebel bases. Displaying the schematics, the droid is shown to be heavily armored and extremely dangerous. Fulcrum also reveals that they can impersonate themselves as harmless protocol droids, specially like the one Zeb just found. Then before signing off, Fulcrum reports that one failed to report in and advises Zeb that if the droid remains out of contact the Empire will come after it, jeopardizing the whereabouts of their base.
Meanwhile, AP-5 and Chopper are Showing the droid around, when Zeb shows up armed with his Bo-Rifle. He warns them to step away from the droid, just as it starts to remember its programming and deploys its true form. Zeb opens fire and the droid attacks. The droid is revealed to be, as Fulcrum warned, well armored and very tough. Chopper tries to take it out with his shocker to no effect. However, Zeb manages to damage it and it retreats, leaking fluids. Knowing what might happen if the droid reports back to the Empire, Zeb, Chopper and AP-5 go after it by following its trail of leaking fluids. The trail eventually ends where they find a dead astromech droid with its power core completely drained and several key components removed. Zeb suspects that the infiltrator droid is trying to repair itself. Chopper is unable to track it and AP-5 suspects that it is still looking for more droids to consume, since the power from the astromech they found was not enough for its needs. This gives Zeb an idea, and instructs Chopper to get its attention and lure it back to him so he can blast it. However, AP-5 points they are in an area housing high explosive munitions, and was not the best place to be firing blasters. So Zeb changes his plan to grabbing it so they can shut it down. With everyone in agreement, Chopper heads out to find the droid. It does not take him long to find it consuming the power of another droid. He gets its attention and runs off with droid chasing after him. Then out of nowhere, Zeb jumps onto the droid and struggles to restrain it. The droid is again proven to be tough to beat. During a physical confrontation, the droid easily out muscles Zeb. However, Zeb manages to restrain it long enough for AP-5 to shut it down. Then just when they think their problems are over, they discover that upon deactivating the droid it has activated its fail safe and is set to self destruct which will vaporize the entire base.
The droid has already started its countdown, set to go off in twenty seconds. However, Chopper manages to temporally freeze the countdown circuit. It gives them the time they need to move the droid to a safer location before it detonates. However, they cannot just dump it because Zeb knows from Fulcrum that if the droid does not report back the Empire will come looking for it. They also cannot allow it to go back, not while it is carrying information on their base. Whipping its memory is not an option and neither is disarming the warhead built into it. The droid is going to explode, and it is just a matter of when. Finally, Zeb has an idea. He suggests they could send it back to the Empire, but with some adjustments that will make the warhead go off when the droid reconnects with the Imperial network. Zeb's plan is to send the droid back to its base and explode before it uploads its data, also taking along with it the other droids leaving the Empire with no clue of which one it was. AP-5 is stunned and finds that a good idea. He makes the necessary adjustments, and before reactivating it sets it to return to its disarmed state. He also initiate its return to base protocol. AP-5 restarts its main system, and then everyone takes cover as the droid reactivates. As AP-5 predicted, the droid returns to its protocol state and peacefully heads back to its ship. Zeb, Chopper, and AP-5 follow it, just to make sure it does leave. They see the droid arriving back at its ship, and before it can contact the Empire Zeb takes out the transmitter. Following its programming, the droid powers up the engines of its ship and flies back to base.
All the droids make it back to the Imperial fleet, including the one that probed Atollon. The technicians inspect the droid that was sent to Atollon, but as a result it reset its warhead and explodes, taking all the other droids and an Imperial Star Destroyer with it. Meanwhile, the Ghost crew return to Chopper Base just in time to hear Fulcrum congratulate the Rebels on dealing with the droid that infiltrated their base, much to the confusion of Ezra, Kanan, Hera, and Sabine. Although they managed to protect the location of their base, in doing so they have narrowed Thrawn's search to the ninety-four possible locations searched by the infiltrator droids.
- Taylor Gray as Ezra Bridger
- Freddie Prinze, Jr. as Kanan Jarrus
- Vanessa Marshall as Hera Syndulla
- Tiya Sircar as Sabine Wren
- Steve Blum as Garazeb Orrelios, Droid Technician #1
- Stephen Stanton as AP-5, Droid Technician #2, Imperial Officer
- David Acord as Imperial Infiltrator Droid EXD-9, Rebel Officer #1, Rebel Officer #2
- David Oyelowo as Agent Kallus
- Lars Mikkelsen as Thrawn
- In the original story for this episode was a smaller B-story that would be occurring while the events of "Trials of the Darksaber" formed the A-story. The story was also going to be focused on Zeb and Rex, rather than teaming Zeb up with AP-5 and Chopper.
- The beginning of the episode is a reference to the beginning of The Empire Strikes Back, where a Star Destroyer deploys Viper Probe Droids down on Hoth to look for Rebels.