The French expression 'entre chien et loup' is a poetic way to talk about dusk, the brief period of time after the sun sets, when the sky is just beginning to get dark. The idea is that there's still enough light to see an animal in front of you, but not enough to tell whether it is a dog or a wolf—and by extension, whether you might be in danger.
Reference: http://french.about.com/od/vocabulary/a/entre-chien-et-loup.htm