Existence of 5-cage implies sum >=15
Existence of 2-cage implies sum <=17
Existence of 8 different 4-cages implies sum>=16
Absense of kropke in 2-cage implies the sum's exactly 16
=> 2-cage is a 79 pair

"The secret" in box 9 immediately places a 3 in the 3-cage cell that hangs outside in box 8
=> its kropke partner must be a 4
=> its cage completes with a 9

black kropke in 3-cage in box 9 can only be 36 with a 7
=> 4-cage in same box is 1258 and the black kropke's 12

Every 4-cage apart from one (box 7-8) has some kind of kropke in, and there's only one 16-sum that does not admit any kropkes
=> cage containing 1357 identified
=> its 3 is placeable

remaining 3-cage in box 8 can only have evens
=> 268 cage identified

4-cage in box 7 may not contain a 3 so is 1267 or 1249
=> the lower cell of the black kropke can only be a 2
=> the 5 in box 7, being the 5 in row 7, can only be in column 1
=> its kropke partner can't be 6, as the cage cannot have 2 5's.
=> the 457 3-cage is fully placed
=> the 4-cage in the same box is 1249
=> its 9 can be placed
=> the 157 3-cage in box 8 places its 7
=> the 1258 4-cage in box 9 places its 5 and 8

double-white-kropke 4-cage in box 6 can only be 234 (with 7) or 456 (with 1)
=> there must be a 4, which can't be in the middle, and is therefore uniquely placed

The 4 in the 5-cage (12346) is placed
=> black kropkes in 5-cage must be 36 and 12
the white kropke in 5-cage implies 6 is above 3, 1 above 2
=> 654 is ruled out from the 4-cage in box 6
=> the 2347 4-cage is fully placed

we now have 2 1's in columns 4 and 5 in boxes 5 and 8 which restricts what can go in box 2

box 2 has an entire 3-cage and an entire 4-cage, and must not place 6 and 3 in different cages. That limits it to 259+1348 or 358+1249
=> the 3-cage contains a 5, and the 4-cage a 1
=> that 1 is in column 6
=> the 15 pair in box 8 resolve
=> the whole 5-cage fully resolves
=> the 3-cage containing 268 fully resolves
=> naked 8 in r7c4
=> box 2 has 259 and 1348 in its cages
=> 7 and 9 placeable in column 5
=> naked 4 in box 8

the 4-cage in box 4 can't have a 3 or 4 in it, so must be 1267, in only one way
=> the 14 pair in box 7 resolves
=> the 5 and 9 in row 6 fully resolve
=> the 3-cage partly in box six must be the 169
=> 8 placeable in box 6
=> 5 placeable in box 5
=> the 3-cage in box 4 must be 358, and resolves completely
=> 9 placeable in box 4
=> the 86 pair in box 7 resolves
=> 178 fully placeable in 3-cage in box 1
=> 48 pair resolves in box 2

1456 cannot go in the 4-cage in box 1
=> 2356 all placeable in the 4-cage in box 1
=> 4 and 9 placeable in box 1
=> 79 pair resolves in box 3
=> 6 and 7 resolve in box 2
=> 1456 all placeable in the 4-cage in box 3
=> 259 triplet fully resoves in box 2
=> 16 pair resolves in box 6
=> 12 pair resolves in box 9
=> remaining 2, 3, 8 in box 3 drop in

Bosh!