As soon as the bell rang for a break,the door opened and in came Mr Black.(这是时间状语从句)
语法：
1 As soon as === the moment 一- -- - 就 -- - -.
2 in came Mr Black.这是倒装句结构.非倒装句是：Mr Black came in.
又如：the boy went out in a hurry.-------Out went the boy in a hurry.