Crooked Was His Cane (Detective Inspector Declan Walsh #19)

Waiting for a taxi can be murder.

Someone is killing London "black cab" taxi drivers.

Seemingly unconnected, but all with the same MO, bodies are being found across the City of London, and only two clues connect them; an unknown killer with a crooked walking cane, and the title to a folk song placed on rolled paper inside their mouths.

Now, DCI Walsh and his team, still reeling after the end of
Harvest For The Reaper
must hunt down the killer, falling into a world of taxi apps, cab driver tribalism, a map of death related to "The Knowledge," and a cold crime from decades earlier, while fighting the potential closure of their unit...

Is this the last case for the Last Chance Saloon - no matter what happens?