(Some talk about the ending - no names named but some details which may be spoilery.)
I haven't really read any 3rd period Queen, but I know what they're like - while they have murders with stunning solutions, the mysteries are supposed to take backseat to the characterization, especially the citizens of the town Wrightsville and Ellery himself. This, however, is slightly different. Thought to be a manuscript from the 2nd period which was scrapped after Agatha Christie released And Then There Were None, then reworked after Dannay and Lee published Calamity Town, There Was an Old Woman is clearly the intricate kind of puzzle from the Nationality Era, but with more interesting characters and a more interesting Ellery - not unlike Halfway House in that regard.
The best part of this novel is seeing the crazy Potts family. Led by the elderly but cunningly tyrannical Cornelia Potts, the family runs the Potts Shoe company, selling shoes to the lower class for decades. She has has six children from two husband's, three kids each. Her first husband Bacchus was kind of loopy until he up and disappeared, and Stephen Brent, his replacement, the exact opposite - he has taken the Potts name himself instead of vice versa, and he's brought his obese war-buddy Major Gotch to live with the family.
Her eldest son, Thurlow, is obsessed with protecting the Potts name and sues people for slander at the slightest joke of which he or his family is the victim. Louella is convinced she's the inventor of the century, and locks herself away to meddle with chemicals and plastics, only coming out do demand more "research money". Horatio, the last child fathered by Bacchus, believes that man is happiest when he embraces his inner child - he lives in a house straight out of Snow White and spends his day writing kids' books and flying kites (Yes, this is exactly as weird as it sounds.)
Thankfully, the Cornelia-Stephen Brent children are much more sane than their older half-siblings. Robert and Maclyn are twins; they look alike, speak alike, think alike, and work alike - the two are Vice Presidents of Sales, Advertising, etc. for the Potts Company and they virtually run the business. Sheila, the youngest, is the only one eager to relinquish her surname. She is engaged to be married to the family lawyer, Charley Paxton - who inherited the legal troubles of the Potts from his own father - but Cornelia won't allow the marriage due to her strange fixation on her older three kids (in this case Louella) and her hatred of her kids with Brent.
The plot starts when Ellery, Inspector Queen, and Sergeant Velie - this trip back once again after quite a while of separation - go to witness Thurlow's 37th slander suit against the unfortunately accused (and unfortunately named) Conklin Cliffstatter after the trial they're meant to be witnesses at it postponed. In attendance are Thurlow and Charley at the plaintiff's table, along with Cornelia herself and her personal physician, Dr. Waggoner Innis. Ellery quickly becomes interested in the family, and when Thurlow renounces the legal system and vows to get vengeance on future slanderers through the code of duello - and surprisingly enough, that next slanderer is his own half-brother, Robert. Ellery, Sheila, Charley, and the twins hatch a plan to replace the single bullet in each gun to be used on the duel with blanks, and it pays off - until the duel itself, when Ellery gives Thurlow the gun, begins the duel as "Master of Ceremonies", and sees Thurlow shoot Robert through the heart, killing him. Clearly, someone involved in the family affairs has replaced the bullet. Thurlow himself, Charlie, and Sheila have solid alibis, while the others do not - and they always could have heard the plan by eavesdropping. It will only be after two additional deaths, but Ellery will crack this strange nut of a case.
About the Christie comparisons - this is nowhere close to the plot of And Then There Were None. Nobody stranded on islands or houses, no mysterious hosts, and as I said, only three deaths instead of ten. If you want a Queen with a high body count, try Cat of Many Tails - I haven't read that one yet, but I hear that one has no less than nine victims. The mystery here is actually pretty decent overall. The clueing is both concrete and abstract - such strange clues as a bowl of cold soup, missing guns which are the same models of the two used in the duel, and a written confession brought into question (that's not a spoiler, since a confession that comes into play three-fifths into the book is probably not the real deal) succeed in dazzling and confusing the readers away from the truth. After a false solution from that written confession, Ellery ambles about a bit before finding a new vital clue and using it to prove an impenetrable case against not completely unsurprising person, and there are some parts about it that I just really love. But wait, there are still thirty pages left, and Queen is not one to do some post-solution falling action, especially with such a puzzle-oriented title as this. Well, Ellery finally realizes the full truth behind the crimes and reveals his findings in possibly the most dramatic way ever, which I will not reveal here. He then does something interesting - he uses the new evidence he's realized not to destroy the previous solution, but to add onto it, and in this way brilliantly shows the cast of characters who is really behind the terrible deeds, and it is indeed a much more surprising choice. Plus, for once the investigating team actually cares about having concrete evidence against the murderer that can get them found guilty in court, and in this case that evidence is not bad at all.
If the book has ended here in the absolute chaos of the penultimate chapter, or maybe halfway through the last chapter, it would be fine. It'd be great! But in the last two or so pages of this book Dannay and Lee do something really weird - don't worry, not weird like The Burning Court, (at least that book's unique ending has a point,) but nonetheless sudden and seemingly without sound reason. All of a sudden they turn one of the (unique) characters in the book into a recurring character from the Ellery Queen radio show, making this whole book a backstory for that character. And they don't even do it well; it comes off so forced! I mean, you have this greatly written puzzle, with strange personages and mysterious murders, and you turn it into a sudden radio-show tie-in for no tangible reason!? Huh!?!?
That gripe aside (and a very big gripe it is, it cost this book a whole star,) this is definitely on of the best Queens in terms of fair-play mystery plotting and one of the best where that intricate plotting meets actually interesting characters. Sure, some of them have only one big quirk which gets capitalized on, but it's better than having 25 suspects who all give their alibis intermittently, show one emotion (if we're lucky,) and the that's it. At least this book made me laugh out loud a couple times.