No sooner… than…
Definition 1 of 1
Pro Tip 1/3Sequential Actions
Use when describing two actions that happened in sequence, almost simultaneously. 
No sooner had she finished her speech than applause filled the room.
Pro Tip 2/3Past Perfect
The first action often uses past perfect tense to emphasize its completion before the second. 
No sooner had the sun set than the stars appeared.
Pro Tip 3/3Immediate Response
Indicates an immediate reaction or consequence to an event. 
No sooner had the lights gone off than her phone rang.