The initial phase of their assignment goes smoothly as they settle into their new roles. However, their cover is threatened when their "neighbors" (the actual criminals) begin to grow suspicious. The primary reason for their doubt is that they never hear any sounds of intimacy coming from the couple's apartment at night. The suspects reason that any genuine newlywed couple would not be so quiet, and their silence suggests their relationship is a sham.
To blend in, they pose as a newlywed couple living in an apartment that serves as a hidden hideout [TMDB]. secret mission sennyuu sousakan wa zettai ni