Returning home, chum entering study is invigorated again (10)

'invigorated again' is the definition.
('animated' can be a synonym for 'invigorated' so perhaps 'reanimated' is OK for 'invigorated again')

'returning home chum entering study' is the wordplay.
'returning' is a reversal indicator.
'home' becomes 'in' ('he's home' can mean 'he's in').
'chum' becomes 'mate' (I've seen this before).
'entering' indicates putting letters inside.
'study' becomes 'read' ('read' can be a synonym of 'study').
'in' backwards is 'ni'.
'ni'+'mate'='nimate'
'nimate' inserted within 'read' is 'REANIMATED'.

'is' is the link.