The tortilla is representative of the Mexican experience, and a curtain is something that separates or divides. The "tortilla curtain" refers to the physical boundary between Mexico and Southern California, and, in a deeper sense, the vast ideological and sociological chasm separating the American citizen and the Mexican immigrant.
The two central characters in the story are Delaney Mossbacher and Candido Rincon. The two men and their families live in close proximity, but their lives are completely different. Delaney has a nice house, two cars, and is financially secure, while Candido lives in a makeshift hut made of garbage and discards, and must struggle everyday just to survive. Although Delaney considers himself to be open-minded and liberal, his philosophy works better in theory than in practice, and when faced with the reality of Candido's presence and need, he discovers that he is more inclined to look the other way and gate himself off from what feels like an intrusion. At the end of the story, both Delaney and Candido find their lives threatened by a flash flood. It is only through sharing this dire experience that the men are able to break through the "tortilla curtain" and discover their common humanity .
The title refers to the border between Mexico and Southern California where Mexicans try to illegally cross into the U.S. The novel contrasts the lives of a wealthy surburban couple with a Mexican couple who have crossed illegally into the U.S. Delaney and his wife live in an upper-middle-class gated community, while Candido and his wife struggle each day just to survive. The "tortilla curtain" becomes symbolic of the differences that separate the lives of these two couples. Mexicans cross into the U.S. to find work and to provide their families with a better life. As is seen with Candido and his wife, however, they are no better off. They live in a hut made of trash that the wealthy Americans have thrown out. Candido keeps turning up in Delaney's life after Delaney hits him with his car in the beginning of the story. It takes a flood that almost kills the two men for Delaney to realize that Candido is a human being.