What is the story of Pentecost? 

The eleven remaining Apostles returned to Jerusalem after the Ascension of Jesus into Heaven. Acts 1:14 says, “All these with one accord devoted themselves to prayer, together with the women and Mary the mother of Jesus, and with his brethren.” During this time, the Apostles chose a replacement for Judas Iscariot. They cast lots between two men,

and the lot fell on Matthias.

After nine days of prayer, the Holy Spirit descended upon the disciples. They heard a sound like a “mighty wind,” and “tongues as of fire” were resting on their heads. Going out, Peter spoke to

 the crowd that had gathered. Even though, just a few weeks earlier, he had denied Christ three times, Peter courageously proclaimed the Gospel. That day, three thousand people believed in Christ and were

received into His Church. (source EWTN)