The British poet, Roy Campbell, kept the original papers of St John of the Cross safe during the anti-clerical activities in Toledo at the outset of the Spanish Civil war. Earlier in 1936 the Carmelites had already sought refuge with the Campbells. As the republican forces advanced on Toledo, they took a trunk to the Campbells with the priceless papers of their saint.
During a search of his house, Campbell made a promise to St John of the Cross that he would translate the saint's poems into English if he and his wife and family were spared. He fulfilled this promise and produced a highly acclaimed translation which he insisted was aided by Saint John of the Cross himself.
I found this story (via the excellent New Advent feed) at Crisis Magazine - go to the article there to read more: The Man Who Saved the Original Papers of San Juan de la Cruz.
In one respect, I think that this story is amusing. St John of the Cross taught that we should be detached from all material things and never seek extraordinary phenomena. He has much to teach some groups today that are influenced by what Mgr Ronald Knox called Enthusiasm. The idea of promising a saint one favour in return for another does rather seem to conflict with the ascetical and mystical teaching of St John of the Cross.
The fact that the saint appears to have granted the favour might suggest that St John of the Cross, while severe on those vowed in religion, was understanding in the case of a family man caught up in the responsibilities of looking after a family and living in the world.
Still, in today's climate of reform and renewal in the one subject Church, St John of the Cross should be a reminder to us not to seek the extraordinary but to progress in the spiritual life by the normal and ordinary means of faith, hope and charity, prayer, penance and almsgiving. There would probably be an excusing cause if the security services are actually searching your house, but the teaching of St John of the Cross would provide the most perfect way.