Revelation 9:1–6 tells what happens when the fifth angel blows his trumpet. This trumpet judgment is more severe than the previous trumpet judgments. A star, presumably Satan, falls from heaven and receives a key to the bottomless pit. He uses the key to release a demonic force of locusts that torment unbelievers for five months. The torment is so severe that people seek death but are unable to find it. The verses that follow describe the locusts and tell what happens when the sixth angel blows his trumpet.
For a more detailed summary select the link below.
“Revelation 9:1” Bibleref.com
The fifth angel sounded, and I saw a star from the sky which had fallen to the earth. The key to the pit of the abyss was given to him.