But why?
There could only be one answer to this query.

His own dishonesty; his secret knowledge of some trickery relative to the funds of the estate.

He had convinced the girl of his honesty, but, more than ever, West believed the fellow a rascal.

His very helplessness to intervene rendered him the more convinced.
These thoughts flitted through his mind, yet not consecutively, as the car left the grounds, and turned on to the main road, leading citywards.
They were still skirting the Coolidge estate, although the house behind was concealed by shrubbery.

The road descending into a ravine spanned by a concrete bridge, and a rather dense growth of trees shut out the surrounding landscape.