She stood apart from the crowd, letting it drift by her to the platform or the street, and wearing an air of irresolution which might, as he surmised, be the mask of a very definite purpose.
There are no more uses of "surmise" in the book.
Show samples from other sources
He has surmised that this is not a friendly visit.
Colleen Hoover -- Slammed
After texting his mom, he started the truck and peeled out of the parking lot, making it back to the ranch a little after four a.m. Seeing the lights on in the main house, he surmised that his mom had either risen early or. more likely, hadn’t gone to bed.