I've deleted all my other UE installs except 4.25.2 and reinstalled Houdini 18.0.532, ticking ‘install engine for Unreal’ on install.

The installation instructions claim simplicity - the plugin will be available in Unreal.

This should mean I can drag/import a hda/hdalc into UE4 and use it, but it's not appearing in the plugin list in UE, nor is it copied to the folder the installer says it should be in: “C:\Program Files\Epic Games” has nothing in it at all, the folder is empty but Unreal works!

Following these instructions around in circles:
https://www.sidefx.com/docs/unreal/_getting_started.html [www.sidefx.com]

I have it working in version 4.24.3 & 4.25.2, although I normally stay a version or two behind and am currently working in 4.24.3.

Maybe you don't have the plugin enabled?

Hi,

If the plugin doesn't show up in Unreal, then it likely means that the installer failed to locate UE4, and that you'll need to copy the plugins file manually.

Copy the “HoudiniEngine” folder in the engine/unreal/4.25 directory (in your houdini install)
to the Engine/Plugins/Runtime folder of your UE4.25.

Launch UE4, and you should see the HoudiniEngine plugin appear in the plugins, like in FDX3245's screenshot.