In Chapter 8, the Lyte family are forced to quickly leave Milton, where they have a country seat, and return to Boston because, as Mrs. Bessie knows in advance, the Sons of Liberty are planning to tar and feather Mr. Lyte. Mrs. Bessie, the Lytes' housekeeper, secretly works for Sam Adams, so she has advance knowledge of this attack. However, she takes pity on her employers and warns them before a mob of Patriots attacks them.
When Johnny visits the Lyte house in Milton with Cilla to get the silver she forgot, he finds the coat of arms smashed above the Lytes' door. He thinks, "the poor people of Milton had had enough of that rising eye" (page 189). He sees evidence that the Lytes had been surprised suddenly and that they had left their dinner in haste, as their uneaten food is still on the table. Mr. Lyte had a nearly fatal attack when he heard the mob, and he "turned purple and fell" (pages 187-188). He is being tended to by Dr. Warren, who tells Lavinia Lyte that her father must never be worried or upset again.
I think that the answer you are looking for is early in Chapter 8. In Chapter 7, the Lytes go out to Milton. But in Chapter 8 they come hurrying back to Boston. They have to hurry because a mob of Patriots has attacked them and is chasing them. The Sons of Liberty knew that Merchant Lyte was a prominent Tory and they had been hoping that he would come out to Milton so they could attack him.
Merchant Lyte is "desperately sick." When he saw the mob, at some point, he "turned purple and fell." He is so sick that Dr. Warren is called to tend to him.