Crossword Genius

Had amassed, when they met (3,8)

Ross

I believe the answer is:

got together

I'm a little stuck... Click here to teach me more about this clue!

'met' is the definition.
('get together' can be a synonym of 'meet')

'had amassed when they' is the wordplay.
I cannot quite understand how this works, but
'had' could be 'got' ('get' can be a synonym of 'have') and 'got' is found in the answer.
The remaining letters 'together' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in the Evening Standard.
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