cloak-and-dagger
     adj : conducted with or marked by hidden aims or methods;
           "clandestine intelligence operations";
           "cloak-and-dagger activities behind enemy lines";
           "hole-and-corner intrigue"; "secret missions"; "a
           secret agent"; "secret sales of arms"; "surreptitious
           mobilization of troops"; "an undercover investigation";
           "underground resistance" syn: clandestine, hole-and-cornera,
            hugger-mugger, hush-hush, on the quietp, secret,
            surreptitious, undercover, underground
see also:
clandestine hole-and-cornera hugger-mugger hush-hush on the quietp secret 
surreptitious undercover underground