There are two primary schools of practice regarding the passage of time in juvenile serial literature. One is to embrace the passage of fictional time, trace one's juvenile protagonists on the rest of the bildungsroman trajectory, and introduce a fresh generation of juvenile characters to retain appeal to one's younger set of readers: this approach is exemplified by L. M. Montgomery's Anne books, with their succession of adoptees, pupils, children and neighbors' children. Conversely, one may choose to defy fictional time and keep one's protagonists eternally frozen in a single year of their lives, which is the safer and more commercial approach, although it does tend to strain credulity at some point; witness the Baby-sitter's Club, or, even more hilariously, the California Diaries spin-off, which attempts to have it both ways in a supremely implausible manner.
Helen Cresswell, with a mad genius worthy of a Bagthrope at their best, has invented a third and entirely different way. Beginning with Bagthorpes Abroad, each successive Bagthorpe book picks up immidately where the previous one left off, not allowing any precious fictional time to escape. Furthermore, each book in this sequence appears to cover ever briefer periods of said fictional time, in what might be termed Zero's Paradox, only reaching something that might be considered an ending in a scarcely-printed tenth book, which after Cresswell's death must be considered final. (I haven't been able to justify paying between $50 and $250 for a copy of this book and no institution is willing to lend it to mine, but I heard that it is inconclusive and unsatisfying.) These later books are linked by an unbroken chain of causality, which is no doubt why when Oxford University Press brought the Bagthorpes back into print, they stuck to the undeniably excellent first quartet.
This time dilation is perhaps at its most pronounced in The Bagthorpe Triangle, where it becomes a positive leitmotif, most fully expressed in this concluding epitome:
What was truly remarkable was that the Bagthorpes had achieved all this in a single day -- less than a day. From that fatal sucked-up sock to the welter of incident described (in part) on the six o'clock news, the fingers of the clock had circled perhaps ten hours. [...] Let us recapitulate:
1. Mrs Bagthorpe utters a Primal Scream and disappears into the Bagthorpe Triangle.
2. Mr O'Tool disappears into the Bagthorpe Triangle.
3. Mr Bagthorpe loses his car and is arrested on suspicion of his wife's murder, and on a charge of assaulting a police officer.
4. The Knaresborough Knifer is sighted in Mrs Fosdyke's living room.
5. A suspect device is sighted in Mrs Fosdyke's living room.
6. An entire county's emergency services is put on alert, and several teams are deployed in Coldharbor Road.
7. The Bomb Squad is called in.
8. Mrs Bagthorpe (still believed to be in the Bagthorpe Triangle, but actually in Coldharbor Road) develops full-blown amnesia.
9. Mr O'Toole, in his alter ego as eccentric millionaire, is reported missing to the police, and described as wearing an orange and purple frock.
10. Mr O'Toole (still believed by the Bagthorpes to be in the Bagthorpe Triangle) is arrested wearing stolen clothes, and on suspicion of being the Knaresborough Knifer.
11. Aunt Celia, already having a Phantom Pregnancy, is now expecting Phantom Twins (who themselves could be loosely described as being in some kind of Triangle).
12. Max Fosdyke, on the run from the police (and long consigned by his mother to a more or less permanent Triangle) fetches up at his mother's house. His sudden reappearance nearly finishes her off.
The book concludes, portentously, "The Bagthorpe Saga will continue ...", and it did, a bit. Would that it had continued further.