As he does his late Christmas shopping on December 24, Eric Masterson frets over all the troubles that have come his way since he became the new Thor (issue #432). As he is lost in his own misery, he fails to notice a lady shopper pulled into an alley. Startled back to the present by her scream, he rushes to her aid; she claims a monster stole one of her gifts. Eric rushes into a nearby alley and changes into Thor, the better to search from the air but he doesn’t spot the villain. Changing back to Eric he goes to his ex-wife Marcy’s apartment where she and her new husband Bobby Steele are giving a lavish holiday for her and Eric’s son Kevin. He shares a tender moment with Kevin then leaves hastily…. To take his mind off his troubles he changes to Thor and searches for the holiday bandit. Shortly, another shopper is mugged and a single present is stolen. This time Thor is on the scene but he is shot out of the sky by a twin laser blast. Landing hard on the ground, he looks up to see a green furry monster dressed in an ill-fitting Santa Claus costume, uttering the word, "Groonk!!" He grapples with his weird foe and the two crash through the wall of a nearby department store. As the shoppers try to continue their mad purchasing spree, the hero and the horror throw punches and the Groonk fires laser blasts from his eyes. The battle is brought to a halt by a dog with a fake antler tied to its head, barking at the Groonk. The monster immediately calms down and follows the dog into the sewers, with Thor in hot pursuit.
Meanwhile, Jackie Lukus stops by Eric’s apartment and finds the place a shambles, with Jerry Sapristi trying to restore some order. The two receive an even bigger shock when Captain America stops by, looking for Eric….
Chasing the Groonk through the sewers, Thor discovers a community of homeless people living there. A little girl named Cindy Lou explains that the Groonk is their protector and normally a nice person. When she read him a Christmas story, the brute decided to provide his homeless friends with a real Christmas so he went out stealing presents, since he didn’t know any better. They promise to return everything the Groonk stole and plead with Thor not to take their friend away from them….
Later Eric stops by the hospital where his friend Susan Austin lies in a coma. As he expresses his affection for her, she suddenly awakens—a Christmas miracle. As he exits the hospital he is met by Captain America, who offers him lodging at Avengers Mansion. Cap also questions him about the Christmas bandit but Eric will only say he made a judgment call; Cap warns him not to make any more lapses in judgment and leaves. Dejected, he returns home to discover all his friends have gathered to give him a big Christmas party.