Just completed this but I can't, for the life of me, figure out the significance of "next" in all of the across clues. Any illumination shone, will be greatly appreciated.
Doubtless I'm being particularly dense.
For a less explicit hint. 1a contains an abbreviation for the first of a very familiar series, and all subsequent across clues follow the series through in a similar fashion twice.
Thanks BuzzyBee, It's finally dawned and of course I can't believe I didn't see it earlier. I groaned audibly. At least I resisted fifteensquared this time.