When telling a story in the past timeA concept which is related to our perception of reality; that part of existence which is measured in seconds, minutes, hours, days, weeks, etc., if an eventA general term expressing that somebody or something does something or that something happens. E.g.: An apple fell on Isaac’s head. quickly follows another, these adverbA part of speech that modifies verbs, adjectives, adverbs and conjunctions. E.g.: I could hardly utter a word. ("hardly")ials and partial inversion is used to express the first event. In the invertA structure in which a verb or an auxiliary precedes the subject. E.g.: "Here comes the sun."ed clauseA group of related words containing a subject and a verb. usually past perfectThe aspect expressing completion. E.g.: He’s finished university. is used. With no sooner … than, however, we can also use simple past.

Hardly had I arrived home when the telephone rang. (= I had hardly arrived home when the telephone rang.)

Scarcely had she finished reading when she fell asleep. (= She had scarcely finished reading when she fell asleep.)

Barely had they won the match when the coach had a heart attack. (= They had barely won the match when the coach had a heart attack.)

No sooner had the company launched its new product than it went bankrupt. (= The company had no sooner launched its new product than it went bankrupt.)

No sooner did they realize that they had made a mistake than the company went bankrupt. (= They no sooner realized that they had made a mistake than the company went bankrupt.)

It may be difficult to memorise when it is when and when it is than. If so, remember that sooner is the comparative form of soon and in comparisons we use than. This type of inversion is basically a comparison.

No sooner had I opened one doll than I found another one nested in it.

Diagrams

Partial inversion after negative adverbials
Partial inversion after negative adverbials NEVER, RARELY, IN / UNDER NO CIRCUMSTANCES, IN NO WAY, NOT ONLY ... BUT ALSO, LITTLE etc.