The speaker addresses a mother and begs her to return, but the request is strange and a little chilling. "Come back to the gun" asks her to leave something and go back to a place defined by a weapon. The title, "Defector," suggests she has switched sides, abandoning one world for another. Here, that other world seems to be "the country of the deer," a wild, quiet place away from guns and the people who carry them.
The poem is only six lines, and its short, plain commands make it feel urgent, almost like a plea or an order. It's hard to tell whether the speaker is angry, afraid, or grieving. Perhaps all three. Judging by the imagery, the mother may be crossing over into nature, or into death, and the speaker can't follow. The mood is stark and uneasy, with a sense of loss. The deer are gentle, the gun is not, and the speaker seems caught between them.