close in

verb

1. To enclose, lock up inside something.
2. To come or approach nearer to someone being pursued.

   “The police had not yet caught the thieves, but were closing in.”

   “Keep refining your estimate, and you will gradually close in on the right answer.”

3. To become closer, surround.

   “Then we pass through Bebington station, and, entering a cutting, become aware of the usual signs of approach to an urban area—buildings closing in, an all-round increase in smokiness, and the application of brakes.”