infiltrate

infiltrate verb [ T ] uk/ˈɪnfɪltreɪt/ us
to secretly join a group or organization so that you can learn more about them

проникать, внедряться
A journalist managed to infiltrate the gang of drug dealers. infiltration noun [ C,U ] uk/ˌɪnfɪlˈtreɪʃən/ us

проникновение, внедрение
infiltrator noun [ C ]

шпион