Essek is with the Nein while they are traveling with the Tombtakers. So far he's kept his feelings for Caleb to himself, but watching Lucien openly flirt with Caleb gets under his skin. Then they stay the night in the tower and Lucien suggests Caleb share his bed.

+ Lucien being possessive of Caleb (and Beau) because of the eyes.
+ Caleb has unresolved feelings for Molly (Lucien preys on that).
+ Either Caleb and Lucien do hook up and Essek suffers. Or Essek confesses and he Caleb get together.