"A Triangle in Shadows" is an umbral vampire lair suitable for a party of four 15th-level characters. Magic weapons are highly advised. This adventure can be completed in one session. The City Fallen into Shadow is the domain of the fiendish umbral vampires, and they are rarely found outside it. But one named Caragorn has fled the city after coming between the lovers Philadon and Zenobia. Philadon and Caragor, however, are secretly meeting at Caragorn's tower behind Zenobia's back. Zenobia suspects them of collusion, and is seeking out the two male umbral vampires to get revenge.