Chris Klie noted that, of the twelve maps he submitted to id for their Master Levels for Doom II project, only two were rejected for quality concerns, Device One and The Enemy Inside (the rest due to time constraints and the 20 map ceiling). Neither are my least favorite Master Level offerings, but I'm just one person of several billion. The name of the map conjures up narrative questions. Where is the enemy inside of? Is Doomguy clearing out demons from underneath a base with a previously unknown secret? Or merely infiltrating an already-inhabited fortress of Hell? Either way, The Enemy Inside is a short level that takes place entirely indoors, featuring a heavy wood theme, with ample brown metal struts.
Architecturally it's an odd duck, looking more like one of the later Doom II levels. There's some cool stuff like the opening room, the skull hall's metal supports and a sewer section replete with torches and some nice lighting, as well as a few marble sections to help break things up. There's a nice tricky arena at the end which requires a bit of puzzle-solving to clear. Lining the main chamber with the red-eyed gargoyles is kind of a dud, though, and there's a lethal player-initiated trap if you press the wrong button in the blood pit area.
It's not a difficult map, even though it features several arachnotrons and a Cyberdemon. It's partly due to with the powerups; you'll have a berserk pack, six invulnerabilities, three megaspheres, a soul sphere and combat armor with which you can hack out most of the map's rough parts. Granted, you can make things harder on yourself depending on which way you attack the sewer section from or whether you even explore to the rocket chamber. I do like the hallway that leads to the final encounter. The lost souls mix things up and flipping the skulls to raise the complete staircase is neat, if a little redundant.
The Enemy Inside is a nice map from Klie. I think it has way too many powerups for the challenges presented within but it's got some decent action and may actually afford some difficulty for those not in the know. It's also in a style different from Klie's usual techbase flair, making it a nice diversion from the rest of his Master Levels submissions. I recommend it to fans and those looking for short, competent Doom II maps.