The Coin of Life
Lucas ambushes Alex Hade, Jade Wang, Jess Wang and Kylie Harper. He and Alex exchange words. He reveals that his forces have captured all the other Guardians except Sam and Darren, who later come to disrupt. The groups begin to battle, with Lucas taking on Alex. He tries to use the water against him, but it is firmly under Sam's control. Alex beats him easily, much to the surprise of everyone. Instead of killing him, Alex makes a deal with him, which Lucas is later shown to have kept. Alex respects him for this.
They meet again at the Louvre. When he sees Alex Lucas shrugs, appearing to let Alex know that he kept his end of the deal. He takes part in the battle. He is one of many killed in the blast.
Lucas appeared to be very cocky when he first met Alex Hade. Though he is also shown to be honorable, after keeping his end of the deal and in many ways thwarting Geron's plans in his refusal to go after Alex. According to Geron, Lucas was afraid of Alex.
Alex reaches the peak of his depression when he learns of Lucas' death, which indicates that he actually liked Lucas as a person.
Alex apparently wasn't very impressed or threatened by Lucas' appearance.