Mr. McLintock is Head Gardener at Chrestomanci Castle under Gabriel de Witt. When the Wraith's abduction of Gabriel and attack on the Castle leaves everyone scared and appalled, he tells Christopher that although he and his staff know mostly about growing spells and similar kinds of magic, they are willing to help in any way they can. Christopher tells them to grow spiky plants, thistles and so on to plug in any gaps in the outer walls & hedges, and to do everything they can to make sure that neither the Wraith nor the Arm of Asheth can get into the grounds to do mischief.
Years later, he is still working as gardener at the castle when Jason Yeldham, former bootboy, returns from his plant-gathering expedition and announces that he has been married and he and his wife will be buying a house in the neighborhood.