The most common and most likely answer to this crossword clue is the 12 letter word SHAREHOLDING
I've seen this crossword clue in The Daily Telegraph
S
H
A
R
E
H
O
L
D
I
N
G
Buddy explains!

The straight part
We know that "Investment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case investment = shareholding.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SHAREHOLDING mean?
SHAREHOLDING noun- The owning of shares
- The amount of capital held as shares
- Owning shares.