Mrs.Robert herself did not know why.
The reader, however, will know why, and will understand how it was that Mrs.Robert was in the dark.

The attorney, though he was suspicious, though he was frightened, though he was, in truth, very angry with this new brother-in-law, through whose ante-nuptial delinquencies so much sorrow was threatened to the Bolton family, nevertheless kept the secret from all the Cambridge Boltons.

It had been necessary to him to seek counsel with some one, but he had mentioned the matter only to his brother William.

But he did not wish to add to the bond which now tied him to Folking.

If this horror, this possible horror, should fall upon them,--if it should turn out that he had insisted on giving his sister in marriage to a man already married,--then,--then,--then----! Such possible future incidents were too terrible to be considered closely, but with such a possibility he would not add to the bonds.