In the article I would like to discuss the problem of collaboration of the Catholic priests with the Security Service (Służba Bezpieczeństwa - SB) as is shown by the example of the agent under pseudonym "Bagiński". It is documented that the Reverend Stanisław Krynicki from diocese of Lublin cooperated with the Voivodeship Office of Public Security (Wojewódzki Urząd Bezpieczeństwa Publicznego - WUBP) in Lublin from 1947 to 1962. The Reverend is an example of a frustrated priest who sought a chance to rise to a higher position in the Catholic Church hierarchy thanks to his cooperation. He was one of the most valuable collaborators and his work was very harmful. Many people suffered because of his actions. Krynicki's cooperation unveils the mechanism of the destruction of the Catholic Church in Poland by the Security Service of the People's Republic of Poland (Polska Republika Ludowa - PRL) on the diocese level. The case of the Reverend Stanisław Krynicki enfeebles myths about the heroic role of the Catholic Church in Poland. It proves that during PRL's period priests not always remained steadfast in their beliefs. There are some undoubted cases of priests' collaboration which was very dangerous to the functioning of Polish Catholic Church. Such was also the conduct of aforementioned Reverend "Bagiński". It is heartening that the number of collaborators within the whole diocese was scanty (only about 10%).