The scheduled visit of the three seers to the Cova da Iria in the mountains of Portugal where they had by blessed with an apparition of Mary every month on the 13th since May was not allowed to happen as planned. The intervention of the administrator of the district, Artur de Oliveira Santos, a prominent Freemason, had imprisoned the children on August 13, and for two days he used many means, including the threat of boiling them in oil, to pry from them either the Secret itself, or a confession that they were lying.
Courageously the children refused to betray their confidence and remained steadfast under every tactic used. In fact, believing that they were soon to be killed, they were full of joy at the thought of soon being in Heaven. This willingness to suffer martyrdom is another proof of the truthfulness of the Message. Realizing that he was getting nowhere, after two days the administrator released the children.
While the seers were being held on August 13, Our Lady still came to the Cova da Iria and manifested Her presence to the large crowd of 10,000 or more. One faithful woman described the scene:
The clap of thunder was more or less similar to that of the preceding time. Some say that it came from the road, others from the holm-oak …. It seemed to me that it came from very far. Everyone kept quiet, frightened …. At the clap of thunder there followed lightning, and at once we began to notice a small cloud, very pretty, white in color, very light, which hovered some moments over the holm-oak, then rose towards the sky, and disappeared in the atmosphere.
While looking around us, we observed a strange thing, which we had already seen the previous time, and which we were going to see again in the future. The faces of the people had all the colors of the rainbow: pink, red, blue … The trees did not appear to have branches and leaves but only flowers; everything seemed laden with flowers, and every leaf appeared to be a flower. The ground was covered with squares of different colors. Clothes were also of every color of the rainbow.
(Adapted from: http://www.fatima.org/essentials/facts/1917appar.asp)