The last two letters for today begin a note of urgency which will grow. The doctor writes to the family they must come; and he's someone no-one can accuse of an obvious interest or a motive in lying (Ross Penguin Let 461, pp 1332-3); Belford writes Morden telling him that if he doesn't come soon, he'll never see Clarissa alive (Ross Penguin Let 462, p 1333).
I thought the doctor's letter was good. We are supposed to see it as effective-- something the mother and father will hear. Richardson's still throwing off presences.