Show about Henry and Mike's ghosts (8)
I believe the answer is:
phantoms
'ghosts' is the definition.
(I know this)
'show about henry and mike's' is the wordplay.
'show' becomes 'panto' (pantomime).
'about' is an insertion indicator.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'and' is a charade indicator (letters next to each other).
'mike's' becomes 'M's' (phonetic alphabet: alpha, bravo, charlie etc.).
'panto' enclosing 'h' is 'phanto'.
'phanto'+'ms'='PHANTOMS'
(Another definition for phantoms that I've seen is " Spectres, ghosts".)