S2:E8: The Communicator: After an away mission to a planet of a pre-warp civilization, it's discovered that Malcolm returned to the ship without his communicator. So Captain Archer & Lieutenant Reed must return to the surface to retrieve the advanced technology before it's found.
When the Captain and Malcolm return to the surface, not only do they find that the communicator has been found, they're also taken into custody and questioned by the local military. Unfortunately, after some brute force is used in questioning, their disguises become apparent as their blood color does not match the blood of the inhabiting species.
When they're taken in for full biological scans, it becomes even more apparent that they're not from around there. As their phase pistols and communicators are further investigated, and Hoshi is able to intercept radio communications from the surface indicating that the away team is set to be executed, the Enterprise crew begin to put together a rescue plan.
Another great episode of as I like to call it, "laying the groundwork" for what can go wrong on an away mission to a less-technologically developed world and the consequences it can have since the military personnel Archer & Reed dealt with believed them to be genetically-engineered spies from a rival alliance.