Plain to see (8)
'plain to see' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for overt that I've seen before include "Done or shown openly" , "Not locked away" , "Done in an obvious way" , "Open, not secret or hidden" , "Open, up front" .)
(Other definitions for manifest that I've seen before include "Express" , "Obvious, like ship's cargo list" , "Clear, obvious" , "Ship's document; plain" , "Conspicuous; cargo list" .)