close in phrasal verb ( see also ↑ close )
1 . to move closer to someone or something, especially in order to attack them:
The snake closed in for the kill.
close in on/around/upon etc
enemy soldiers closing in on them from all sides
2 . if the night, bad weather etc closes in, it becomes darker or gets worse:
The sun had set and dusk was closing in.
3 . if the days close in, they become shorter because it is autumn