Lyric discussion by ExistingPerson 

Cover art for Undercover Martyn lyrics by Two Door Cinema Club

My own interpretation of this song is about this guy who meets this hooker, street name is "Martyn". The lyric "basement people to the basement" is talking about how she sleeps or does her business in the basement. And the line "she spoke words that'll melt in your hand/words of wisdom" is maybe talking about how the guy used to know Martyn when they were younger. "You hid there last time/you know we're going to find you" is possibly about Martyn hiding from her old friend because she doesn't want him to see her like that. "Sick in the Carseat because you're not up to going", she isn't up to what she has to do with one of her customers so she feels sick to her stomach. "Out on the main streets, completing your mission" this line is what set me on this idea for the song. Martyn is out on the streets completing her mission of getting money. I know nothing about the band I just like the song. So that's my take on it. Let me know what you think.