He first appears calling Paul by the phone to tell him that Carol and Joanna are taken to a hospital, and tells him to meet him there. He then meets Paul at the hospital where he tells him that they were attacked by "two or three men", according to Carol's information to officer Joe Charles. Jack is later seen at Joanna's funeral with Paul and Carol, who's in a catatonic state from the assault.
Later, when Paul visits them in Jack's apartment, Jack tells him that a psychiatrist recommended to have Carol moved to an another environment, so she wouldn't have any reminders of that day. Paul agrees, and tells him to call him everyday about Carol's condition, since he's leaving to Tucson.
After Paul returns from Tucson back to New York City, Jack meets him at the airport. Jack then tells Paul that Carol is in the hospital after she returned from the shore, which upsets Paul, since Jack didn't tell him that earlier. They visit her in the hospital, where Jack then tells Paul that the doctors recommended to have her transferred to a sanatorium in Long Island.
After placing Carol to the sanatorium and returning back to New York, Jack expresses his frustration about the life in the country. Paul then asks Jack about the "old American social custom of self-defense", to which Jack replies that they're not pioneers anymore. Paul then asks what are they, if they're not pioneers, to which Jack unsurely answers "civilized", which only annoys Paul slightly.
Jack later visits Paul at his apartment, which is restored back to normal, with Paul behaving more happily, which confuses Jack. Jack asks Paul if he wants to know how Carol is doing, but Paul replies that he already knows how she is, since he visited her yesterday. Jack then asks him about his behavior, only to Paul ask him if he's supposed to "moan and groan for the rest of his life". He then prepares lunch for Jack.
He's not seen or mentioned in the sequels afterwards, but it's possible that he continues to live in New York City.