Though aired in 1975, "Mother's Deadly Helper" has aged well, and definitely raises issues applicable to today.

Anthony Zerbe plays Lester Smith, a vigilante who shoots criminals dead who escape punishment through legal technicalities. He makes contact almost immediately with McGarrett after his first murder, through a letter sent "special delivery". It is not clear how the letter could have been delivered so quickly, given that the murder had just occurred less than an hour prior, and the letter makes reference to how Smith felt when the verdict in court was read. (Smith shot the released criminal within minutes of his acquittal.)

Smith's letter is full of grammatical errors, and his character is clearly very uneducated, perhaps an early school dropout. While Smith is a fanatical law-and-order right winger, McGarrett makes a speech after receiving the letter that "Right or left, the lunatic fringe is ready to take things into its own hands, thats one thing they share in common." This line was likely inserted into the show to make it clear that the episode wasn't an attempt to bash right wingers, though nowadays Hollywood unabashedly does that all the time! (McGarrett was right when he said that, and even 44 years later, that remains very true!)

Smith owns a primitive coin-op arcade called "Jollyland", which mostly features shooting games.

As Mike pointed out in his review, McGarrett is very inconsistent with his handling of the letters. Sometimes, he exercises the utmost care not to get his own prints on the letter, and other times, he grabs the letter and envelope without a care!

McGarrett appears on the talk show of left winger Freddy Dryden (Casey Kasem), debating law and order matters. While, unknown to Dryden, this is a ruse in order to lure Smith to reveal himself to McGarrett, their debate seems to be real. McGarrett has a lot of disdain for Dryden, and Danny pointed out initially that McGarrett once said he'd "rather be dead" than appear on Dryden's show. Again, this seems somewhat of an attempt to appeal to the audience on both sides of the political spectrum, as the criminal is a right-wing nut, but McGarrett clearly has disdain for the left-wing talk show host.

Smith tells McGarrett to be at a certain pay phone, where he will receive a call. This was back in the day when pay phones were common, and could receive calls! Nowadays, the few remaining pay phones rarely take incoming calls (this started to change in the 1990s).

Smith engages McGarrett in a clever loyalty test, where he supposedly agrees to meet him at a cemetary, but instead pays an unemployed man to hand McGarrett a note identifying himself as Mother's Helper, telling the man it's "a joke". However, Smith planned the whole thing very poorly, also being present at the funeral, and having a hard time escaping when they seal off the cemetary. Somehow Smith escapes without being identified by the man (how?), but his car is located, the gun is found, and it's registered to "Cord McKenzie". Thanks to this test, Smith becomes aware that McGarrett isn't actually on his side.

Smith's location is finally deduced by McGarrett and Che by running one of the phone calls through an "oscillograph", which isolates the background noise. However, both men take far too long to figure out the fairly obvious background noise of machine gun fire, wooden pins, and bells, being connected to an arcade.

McGarrett tells Smith, "I'm just a cop" when Smith calls him a traitor. The final scene is interesting, where Smith says he'll get out on parole and kill McGarrett -- the exact same parole he had been railing against the entire time.

This was actually a very good episode, though it lacked suspense because we already knew who the killer was, and we knew his motives. The only real fault came from the plot line of Smith deciding to graduate from killing criminals to kidnapping (and presumably killing) "bleeding heart" judges. Clearly this change in M/O was to make Smith less sympathetic to the viewer. If he were just killing horrible criminals (rapists, murderers), the viewer might identify with Smith and root for him, but it becomes much easier to root for his capture once he's going after judges.

This was kind of a lazy way out for the writers, though. I would have preferred they left Smith simply going after acquitted criminals, even if it made him a more sympathetic character. If it really was necessary to turn him into a "full" villian, they could have had him mistake a truly innocent man for a guilty one, and Five-O would have had to catch him in time.

I still really liked this episode, and thus still award it four stars (out of 4).