His eyes came to rest on Isabelle and Alec. A faint shiver went through Alec, as if something had plucked at his nerves. Jace's father's words were perfectly ordinary, even polite, but there was something in his blank and predatory gaze that made Alec want to step in front of his sister and block her from Valentine's view.
(City of Ashes by Cassandra Clare, pg. 360)