Mysteries have always had their share of older protagonists, but Too Old for This introduces us to a unique – and deadly – variant of the irascible elder.

The knock on her door is completely unexpected. Lottie Jones doesn’t have visitors. She plays bingo on Thursday nights and goes to church on Sunday morning. She is boring in her old age, knows it, and likes it that way. The girl on her doorstep is an unwelcome intrusion.

Plum Dixon runs Reboot Productions, a website where they “specialize in telling the story behind the story.” She wants to interview Lottie because many years ago, Lottie was Lorena, a single mom accused of being a serial killer. The case against her was eventually dropped, and Lottie changed her name, moved, and began a new life. Plum thinks Lottie’s story would make an excellent docuseries, and intends to go ahead with or without Lottie’s help, but she would love an interview. Instead, Lottie bashes her in the head a few times with an old metal umbrella. Once the girl is dead, she goes about the serious business of cleaning up the mess and getting on with her life.

Of course, that’s easier said than done. It doesn’t take long before people – including a rather pesky detective – are hovering around Lottie. She was the last person to see Plum alive after all, and that young woman’s disappearance is completely out of character. Lottie doesn’t resolve her problems with murder anymore, but then again, old habits die hard…

If you are looking for a believable, realistic mystery, this isn’t it. A septuagenarian killer who has to schedule her crimes around cooking for bingo night and shopping for a retirement home while also dealing with her son’s second wedding is darkly humorous but not in the least credible. That’s okay. Lottie is an unrepentant, irreverent grandmother who is a delightfully fun villain. The author keeps the pacing brisk and throws in just enough authenticity – such as Lottie’s frustration with how hard modern technology makes it to get away with anything – that the story breaks disbelief with a wink and a smile. It’s ridiculous but also entertaining and mesmerizing.

Ms. Downing also nails the characterization. We receive enough backstory on Lottie to keep her from appearing too monstrous, but no attempt is made to portray her as completely sympathetic. The author does a nice job of weaving the biggest weakness of the narrative – Lottie’s age – in humorous chunks throughout the tale. Lottie is doing all manner of mischief, but her enjoyment of that is seriously curtailed by her failing memory and increasingly frail body, and we are given a good sense of both her violent personality and the fact that she is an old woman who would far rather be sitting in her recliner than dealing with this nonsense. It takes immense skill to write about such a callous, disturbing individual without alienating the reader, but Ms. Downing threads that particular needle perfectly. The secondary characters – Lottie’s nemesis at bingo night, her friends from church, her son, his ex, and his fiancée – are also well depicted.

The plot kept me invested in the story because I needed to see how everything would end because Lottie’s heinous antics and rusty skills mean that she is deeply dependent on luck to get away with it all. I wondered if she could succeed and if I even wanted her to. The will-she-or-won’t-she nature of the story, as well as the increasingly desperate measures Lottie is forced to take, kept me (mostly) riveted. There’s a section towards the middle that dragged a bit, but then a new adversary is introduced, and I was sucked back in.

Too Old for This is dark and gritty, but also wildly entertaining. I recommend it to those who enjoy sinister thrillers that take them to unexpected places.