Andrew is the next-door neighbor of Magid Rupert Venables, and he's a very odd character. A successful inventor, who can explain his inventions in shockingly comprehensible detail, he also seems somehow absent-minded, and when his car stops working, as it seems to do quite often, he shows up at Rupert's door asking for a lift to wherever Rupert's going.
Rupert considers him a pleasant neighbor and a good passenger, because he makes no demands, doesn't insist on making polite, labored conversation, and is willing to be ready to go whenever Rupert wants to leave, and to make his way back home from the destination rather than subject Rupert to the complications of arranging to meet and leave together.
Andrew is quite tall, with large, pale eyes, bleached-looking hair, and the strong bone structure of Scandinavian, although Rupert believes him to be Scottish. He has a slow and meditative way of speaking, and he often looks off into the distance while he thinks through a question posed him.
Rupert ends up driving Andrew to Bristol on the occasion when he succeeds in tracking down Maree Mallory. He also takes him along to Wantchester, even though Andrew comments with a faint smile that a fantasy fiction convention doesn't sound like Rupert's cup of tea.
At a couple of points during the convention, Rupert sees Andrew in the distance, although he never actually catches up with him enough to talk to him. It seems as if he has registered for the con, as he seems to be wearing fancy dress on one of those occasions, but again, since he doesn't speak to Andrew, he can't be sure. It's just one more odd thing about his neighbor that Rupert doesn't really understand until much later in the novel.