Then he sobered.
( Then ( he ( sobered . ) ) )
(ROOT (S (RB Then) (NP (PRP he)) (VP (VBD sobered)) (. .)))
He had sobered up.
( He ( ( had ( sobered up ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD had) (VP (VBN sobered) (PRT (RP up)))) (. .)))