hardly, scarcely and no sooner

These three expressions can be used (often with a past perfect tense, (see here) to suggest that one thing happened very soon after another. Note the sentence structure:

Grammar

… hardly … when/before …

Grammar

… scarcely … when/before …

Grammar

… no sooner … than …

• I had hardly/scarcely closed my eyes when the phone rang.
• She was hardly/scarcely inside the house before the kids started screaming.
• I had no sooner closed the door than somebody knocked.
• We no sooner sat down in the train than I felt sick.

In a formal or literary style, inverted word order is possible (see here).

• Hardly had I closed my eyes when I began to imagine fantastic shapes.
• No sooner had she agreed to marry him than she started to have doubts.