Wander about with son in lodgings (7)
I believe the answer is:
Here is my best explanation:
'wander' is the definition.
('digress' can be a synonym of 'wander')
'about with son in lodgings' is the subsidiary indication.
'about' becomes 're' (common abbreviation for 'with reference to'**).
'with' means one lot of letters go next to another.
'son' becomes 's'.
'in' means one lot of letters goes inside another.
'lodgings' becomes 'digs' ('digs' can be a synonym of 'lodgings').
'res' put within 'digs' is 'digress'.
(Other definitions for digress that I've seen before include "Stray from the point", "Depart from the main subject", "Stray from main subject", "Be sidetracked", "Wander from subject", "wander", "Leave the point", "Go off at a tangent", "Ramble" and "Go off topic".)