Duke Kling was silent for a while after reading her daughter's letter exactly twice.
What he took seriously in the letter was her mention of "the way to protect you and me."
That suggested that she did not leave recklessly for a trivial reason, but with a deliberate purpose in order to eliminate some threat imposed on them right now, which he didn't know at all.
What she said in the letter could be ridiculous. She grew up without knowing politics and turbulence, which made her often play funny games or show troublesome stubbornness.
He suspected she might have concocted a huge trick intended to deceive somebody or cause trouble for him.
But Marianne usually didn't talk about Estelle when she was kidding.
In the letter she clearly said, 'I can swear on Mom.'
He wanted to find his daughter immediately and question her, but he quickly admitted that he couldn't. He also admitted that he didn't need to ask why Hugo and Mrs. Icell didn't inform him in advance.