Why is Mr Dorsets letter a surprise to Bill and Sam?

Mr. Dorset's letter is a surprise to Bill and Sam because it reveals unexpected information about their situation and intentions. They likely assumed Mr. Dorset would be upset or take action against them for their previous involvement in his affairs. Instead, the letter may contain a proposal or request that changes their perspective, highlighting their underestimation of his character or circumstances. This twist adds tension and complexity to their plans.