According to WikiPedia:
Plumeria flowers are most fragrant at night in order to lure sphinx moths to pollinate them. The flowers have no nectar, and simply dupe their pollinators. The moths inadvertently pollinate them by transferring pollen from flower to flower in their fruitless search for nectar.
This is one of many brilliant flowers currently showing on the patio and duping helpless sphinx moths. Of course, they delight us no end, regardless.
You can click on this image for the large size.