The poor performance was most probably down to the all out-scheduling war that ITV seem to have been waging this week, with nightly Britain's Got Talent and Coronation Street.
Obviously we still have to wait for the iPlayer figures, which could bring the secind episode more in-line with the first and, despite the seemingly massive drop in popularity there's still hope the third and final episode of the drama can rebound when ITV's schedule gets back on track.