If you don't know a lot about Elliott Smith, I strongly recommend that you give his music a listen. I recently watched a documentary about him called Heaven Adores You and became completely mesmerized by his music. Elliott Smith released five solo albums while he was alive. Two more were released following his death in 2003 (ten days before Halloween).
Before he went off on his own, he was in a band called Heatmiser. Plainclothes Man is from their third and last album called Mic City Sons. The band was well know in Portland, Oregon but did not achieve wider success. Their earlier albums are very much in the grunge style but their sound changed by their third album, which I believe can be attributed to Elliott Smith's influence.
I love all the songs that he sings on Mic City Sons but I think my favorite is Plainclothes Man. This song is a great example of how, upon first listen, I find it very difficult to predict where he is going harmonically and structurally with his songs. To me, this is extremely refreshing. Also, he is incredibly skilled at working a vocal melody over non standard chord changes while keeping it melodic at all times.
Here are the chords and structure (click on the image to download a PDF).