Let's see... what is this theme? Kind of a word ladder, I guess, but the word is constructed with every theme answer, not changed. The addition of an extra letter in a common phrase creates eight new words:
23A: Equally pensive? INTHOUGHTASMUCH - extra N turns I to IN
30A: Commit a peccadillo? SINSOMESMALLWAY - extra S turns in to SIN
47A: Perform the hit "Things I Should Have Said"? SINGOFOMISSION G/SING
55A: The Police frontman filming a shampoo commercial? STINGINTHESHOWER T/STING
66A: Tying packages, securing helium balloons, etc.? STRINGOPERATIONS R/STRING
77A: The Beatles showing absolute amazement? STARINGQUARTET A/STARING
93A: First weapons used in a knife fight? STARTINGDAGGERS T/STARTING
105A: Surprising group of suspects? STARTLINGLINEUP L/STARTLING
Pretty cool, really, and somehow it seems appropriate to run it on the only day of the year that sounds like a complete sentence if you say it out loud: "March forth." Guffaw. And speaking of guffawing, my favorite themer was SINGOFOMISSION. So absurd.
It seems like there's more white space than usual for a Sunday. The center is kind of circled off, and the entry into the corners is a little tight, but the corners themselves are awfully chunky. I was a little worried at first glance, but the solve went right along. I did have to stop toward the end to figure out the theme to help me get SINSOMESMALLWAY.
I loved LIONTAMING (5D: Performance for which one might grab a chair). Never heard of NEISSE (51D: German border river).
Over to you, Frannie!
I found the theme entries something of a struggle to come up with, but as they say, what doesn't kill us makes us stronger! :)
I had the most trouble with SINSOMESMALLWAY because I didn't know SEGO (Kind of lily) and, although I thought of MARM (School closing?) I kept rejecting it because I was interpreting 'closing' too literally. Derp.
A HATTIP to HORDE, AEROBE, NOISETTE (new word for me, but I'm not much for lamb), STIFFS, LANAI, TBONE, WREST, FEY, and PSHAWS.
I also liked the clues Out of control? (ONAUTO), "Park it" (SIT), Advance look, say (PEEK), and Do with a pick, maybe (FRO).
Putting this building together left a lot of scraps lying around, including SEP, ENG, AMC, MSG, CALI, ICU, GOA, NEG, EMI, and VID. OTC!