Family comes first on “Hawaii Five-O.” From the sense of “ohana” that bonds the elite crime-fighting force together beyond ties from blood relations, to the real family of its members, family means everything. A tiny family squabble starts off this week's May 3 Episode 23 of Season 9, “("Ho'okahi no la o ka malihini" (A Stranger Only for a Day), between fathers Danny (Scott Caan) and Captain Grover (Chi McBride.) The two are debating the expenses and responsibilities of paying for the prom for their beloved children, still devoted to one another.

Family accommodation becomes a sticky subject for Steve (Alex O'Loughlin) who is hosting his sister, Mary (Taryn Manning) for the weekend. Some fans will remember that she used to be Mary Ann McGarrett but now is just Mary. Steve feels slighted that his sister has booked a rental house over staying at his home, never mind that she is highly allergic to cats. Lt. Commander McGarrett already has all he can handle at home with the arrival of Mr. Pickles, Junior, and Eddie, but Mary has their own reasons, apart from allergies, to wanting her own space. Steve cannot conceal his feelings because “the vein” in his neck tells everything.

Lou Grover’s eyebrows do the talking when the secret gets out that Tani Meaghan Rath) and Junior (Beulah Koale) are going to the big wedding, and of course everyone on “Hawaii Five-O” is more than interested, no matter how much Tani defends that the date is just “as friends” and “a plus one.” She even wants them to meet at the event instead of being escorted.

Heroics and casual investigation lead to some surprising conclusions in this episode, and the night ends with much more than slick moves on the dance floor.

A lot more than lunch

Steve is supposed to be off enjoying time with his sister when “Hawaii Five-O” catches the case of the murderer by ridesharing driver and his last fare.

The driver (Andrew Tripo Lee) calls his fiancée, saying he's about to finish his night, but he never lived to see her again when a man named Carter Hill (Scott Nordquist) jumped into the car and orders him at gunpoint to drive. Both men are found shot with the same caliber weapon by morning.

When Steve brings lunch for his sister, she's not at her lovely rental.

She calls him with the story of how she met Ben Miller (John Patrick Jordan) the night before and found him to be “really nice.” She later watched him and the owner of the home in a heated argument, which she knew was about her.

One of the delights of the episode was the appearance of Blake (Miles Emmons), a neighbor boy to Miller. He is really only interested in the case to recover his drone, but he does have photographic proof of shady dealings at night. He also has great detective lingo down, reminding Mary Ann to “Keep up, lady!” Steve gleefully repeats the phrase.

Being the McGarrett that she is, she cannot resist going over to her neighbor Miller's house. She tells Steve to rush over, and that she has something to show him.

He finds her, and the two share a heart-to-heart talk about the real reason she wanted to stay on her own in the rental house.

She had run into an old boyfriend and hoped they could spend time together. Instead, he ghosted her, and now Steve has suspicions about Ben Miller. Mary is crushed by her past poor choices and thinks probably this is another of those. When she finds rain boots along with the cat litter, and no cat in the home, she suspects meth production. Steve relates how he loves and trusts her judgment completely, telling her that she should be proud to be still “in the fight,” which is more than he can say about himself. He reminds her that finding the right person makes all the effort and disappointment of love “worth it.”

Steve is alerted by a wall that really shouldn’t be there, and sure enough, it leads to an entire meth lab, right on target with his sister’s hunches.

A slippery slope

When the investigation leads to Hill probably being high on drugs and definitely not his usual self for the weekend seminar for mid-level managers, the team also discovers that a woman's DNA is on the weapon. She is a waitress, Kira (Amber Lamarca). She and Hill had plans to consummate their feelings, but instead, pools of her blood were in his room, and she was nowhere to be found.

Thanks to Eddie's nose and the pursuit of “Hawaii Five-O” Kira’s scent is tracked to a rock crevasse, and is barely clinging to a tree, and to life. Junior decides he must go down to her, to stabilize her body until help arrives. The danger factor is too much for Lou Grover to see. After a few precarious slides, Junior makes it to her just in time.

Danny quips that “now you know what my life with Steve is like all the time.”

Mary Ann gets a call by the end of the night from her ghosting ex-beau.

The slow dance does it every time

Tani is a vision and her sleek black satin dress for the wedding, and just as she finishes getting ready, Junior is at the door. He insists that this must be a proper gentleman's date, complete with him taking her in his car. They dash away for the nuptials.

Leaving back her bada** tendencies on the job, Tani can't help becoming emotional at the sight of the bride and groom dancing together. She does a little shimmy to let Junior know that the time has come to let loose when “Boogie Shoes” starts playing. The pair burn up the dance floor and make this episode a true keeper.

When the little flower girls come to Junior for a dance, Tani sees Junior in the new light, perhaps reflecting on the firm yet gentle protection she lost when her father passed, and she was forced to bear all responsibility. When one of the bridal party tells her what a beautiful couple they make, Tani again says “we're just friends,” but she knows something feels different.

She goes to Junior, and they share one of the most memorable screen embraces ever on “Hawaii Five-O,” simply, eloquently touching foreheads as they savor these new feelings.

“I was looking forward to it,” Junior tells Tani regarding her invitation and brushing up on his dancing. Fans of this beloved police drama are looking forward to what comes for this new romance, and in the two episodes remaining for Season 9.