Really a great episode. Any show with James Caan is great and this is a living example of that. The term Juvenile delinquent is actually still a widely used term. Leather jackets never quite go out of style when it comes to youths and the characters are actually believable not ridiculous.
First it's Caan who gives a great, great performance as the writer going into an underworld he knows little about to make a book. He pulls of his fake identity "Phil" well beaten up a couple of gang members and earning respect just like any would be gang member would (that's believable). Just like joining any gang we see him go through an initiation getting beat up. The last part of the initiation entails Phil having sex with the gang's beautiful girl Filene played superbly by Lynn Loring. Loring and Caan have great chemistry as the two gang members who fall in love.
Like a classic love story they try to hide their feelings but it's obvious she's smitten with him. Even when his true identity is found out Filene is still in love with him. I don't know how anybody can say the characters aren't believable they were. Unless you've never been in a gang then you would know this is the way it works out.
There are also noteworthy peformances by Walter Koenig and Zalman King but it's Caan whose clearly the star. This episode is a great testament into why he is such a great actor even at this young age. Highly recommended episode.