Everyone is taken aback, missing one left in Spanish city (7)

'spanish city' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'everyone is taken aback missing one left' is the wordplay.
'everyone' becomes 'all' (all people).
'is taken' says to put letters next to each other.
'aback missing' becomes 'ives' (I can't explain this - if you can you should believe this answer much more).
'one left' says the letters should be written backwards.
'all'+'ives'='allives'
'allives' reversed gives 'SEVILLA'.

'in' acts as a link.

Can you help me to learn more?