In the era of Nicholas I, the policy for further unification of the religious life and stricter surveillance over parishioners led to a rise of investigative cases filed against schismatics. The article discusses how the clergy increased their efforts in revealing the facts of “apostasy” of Old Belief among the Orthodox. In the course of these activities, the Russian authorities discovered the imperfection of their own system of surveillance. The paper shows that the active investigation of cases of “apostasy” produced the opposite result: instead of drawing people back from “apostasy” the policy led to an intensification of religious life of various Old Believer communities. In particular, the paper focuses upon inter-confessional marriages between Orthodox Christians and Old Believers. The legal rules of such marriages were often neglected by the spouses and sometimes by the Orthodox clergy themselves. An analysis is provided of the perception of such marriages by secular and church authorities, and by those marriage couples who were pursued as “apostates”.