Seemingly unbelievable events were occurring one after the other.
Last night, Director Koichi had a dream that he made one Youtube hit after another.
One by one, the cities of Europe fell to the plague.
When something is happening next, next (next next next), it's happening in succession, or one by one. Just imagine a line of people going through to get stamps on their heads. The person at the stamp counter is saying "Next! Next!" and then shouting "C'mon people, one by one, alright?"
The reading is the same as the word 次 (so it's つぎ), but this time you do it twice. No strange rendaku or anything like that either, which makes everyone happier.