Genius 217

[MissSpell]

I have got just over half of the solutions in this challenge.
I have one or two theme words going down, but I haven't
a clue where to go from here.
I don't follow the dropping of letters, but I am sure it will
all come right in the end?
The blurb with the crossword is itself quite unsatisfactory
for someone like me.
HELP!

[JJ109]

Each column where there are downwards clues consists of two clues.
Each of these columns has a theme word, where the last few letters of the upper clue are the first few letters of the theme word. and the first few letters of the downwards clues are the last few letters of the theme word. All these theme word letters are not included in the wordplay of either the downwards clues or the across clues

[JJ109]

^^ first few letters of the "lower " clue are the last letters of the theme word

[roslyn251254]

Have a look at the other "genius 217" threads.
All the theme words go down
Far left column and far right column( not the columns of 2d or 8d) spell words out ....far right one ..you have to read upwards...
there is a theme word in every column
6d Extremely unpopular young rascals .....UR (from outside of UnpopulaR) is the only wordplay. Answer is urchins meaning that CHINS is unclued ....combine with the 1st 4 letters unclued in 24d and you have a theme word....

Ask again if you're still puzzled...

[JJ109]

In addition column one and column 15 contain a phrase associated with a chocolate biscuit which gives the theme. The phrase starts in column 1 row 1 with a "P" and works its way down to the bottom Row 15 column 1 (which is also a P). It then carries on in column 15 but working its way upwards

[JJ109]

Incidentally all the letters in the phrase in columns 1 & 15 are unclued in respect of the wordplay for the across clues!

[MissSpell]

That is all VERY helpful, thank you.
You've given me lots to make a go of this!