Keeping the preamble short, as I'm late enough with this as it is: I found this by no means an easy puzzle, setting down my pen somewhere past the 40 minute mark, but I pretty much loved it, possibly my favourite I've done since taking up this blogging gig. 17th century French satirists, classical tribes and conspirators, Egyptian gods, Latin sea creatures and skin maladies, Pakistani mountains, Lawrentian literature, Cockney rhyming slang, the king of ragtime and/or the queen of rock'n'roll... all this and I think a pangram too. Negotiating this puzzle made me feel witty and well-read, as I'm sure the setter must be too. Thanks setter!
FOI 26A, LOI 15A in a massive "aha!" moment. Nice to see some old friends at 13A (surely this word solely appears in crossword puzzles nowadays?) and 20D. A little bit of - hopefully tasteful enough for present company - smut at 28A which I personally always enjoy. Anyway, posting this now without further delay, and sorry to have made you all wait so long already!
| Across |
| 1 | JOPLIN - singer or composer [Janis, Scott]: JOIN [couple] "keeping" PL [place] |
| 4 | VANQUISH - to beat: VAN [head] + QUI ["in Sorbonne, who"] S H ['s hard] |
| 10 | FINNISH - national: FISH [angle] "eclipses" INN [local] |
| 11 | BOILEAU - French poet: "recalled", "every second of" {a}U{b}A{d}E {c}L{o}I{s}O{n} B{y} |
| 12 | YANK -sudden drag: YAK [gas] "pockets" N [nitrogen] |
| 13 | TROTSKYITE - red: OT [books] + SKY [to send up], with TRITE [worn] "at the edges" |
| 15 | SHIFT KEYS -"those pressed to put on caps": KEYS [explanations] "on" SHIFT [dress] |
| 16 | AUDIO - "of speakers?": O [round] "on" AUDI{t} [investigation "that's short"] |
| 18 | BIKER - "one of a leather-bound set?": B [book] + RE K1 [on Himalayan mountain] "returned" |
| 19 | LAUNCH PAD - "great starter": PAD [dwelling] "on" LUNCH [meal] "having consumed" A |
| 21 | THE RAINBOW - novel: (BAR ONE WITH*) ["swings"] |
| 23 | SWIZ - do: WIZ [maestro] "attending" S [Society] |
| 26 | NAUTILI - molluscs: {are}NA UTILI{sed for} "trapping" |
| 27 | IMPETUS - incentive: I'M ["this setter's"] PET [preferred] US ["the Times"] |
| 28 | EXTENSOR -muscle: (TORN + SEX + E ["close to" bedtime]*) ["fooling with"] |
| 29 | ARCHLY - "in play": A RC [A Catholic] + H{o}LY [devout "sacrificing love", i.e. - O] |
| Down |
| 1 | JIFFY - instant: J [judgment "at first"] + IFFY [questionable] |
| 2 | PEN AND INK - double def: hum [Cockney rhyming slang for "stink"], "notes produced by this pair" |
| 3 | ISIS - deity: CR [credit] + ISIS = CRISIS ["Suez, say"] |
| 5 | ARBUTUS - tree: A [ace] + BRUTUS ["run up", i.e. with the R moving ahead of the B] |
| 6 | QUICK MARCH - military command: QUICK [sensitive area] "that" MARCH [part of the year] "is under" |
| 7 | ICENI - old people: IN [home] "coming up" after ICE ["a certain distance"] |
| 8 | HOUSEHOLD - familiar: HOUSE [put up] + HOLD [conduct] |
| 9 | CHARGE - triple def: rush, to fill, ward |
| 14 | STARVATION - "what can come of fast": (A V [verse] IS NOT ART*) ["preparation"] |
| 15 | SUBSTANCE - body: BUS [vehicle] "is turned up" + STANCE [bearing] |
| 17 | DIP SWITCH -"one turns down light": DIPS [sauces] + WIT [salt] + CH [chestnut] |
| 19 | LENTIGO - skin condition: (OIL GENT*) ["applied specially"] |
| 20 | UTOPIA - More work: TOP I ["leading one"] "to break" UA [{act}UA{lly} "in the middle"] |
| 22 | ERUPT - flare: PURE ["not spotted"] "rising over" T ["bow of" trawler] |
| 24 | ZESTY - "like Peel?": ZEST [go] + Y [party's "right wing"] |
| 25 | SPUR - double def: short road, drive |