Exactly what we want to avoid.

I'm in danger of breaching my NDA if I go on actually - for now at least.

In short - point and click was deemed a no-no for various reasons, while text adventure was deemed a yes-yes for others (partially due to lack of sprites etc).
...and this looks pretty interesting actually, TA!

Someone already mentioned Ren'Py, which is a visual novel engine. I don't have much hands-on experience with it or other VN engines, but that might be an avenue to explore with the project and some of them I believe can easily compile for cross-platform distribution. Again, I have no hands-on experience so can't really say how flexible the engines are, but they do seem quite accessible out of the gates.

The two VN engines that I have heard of:

Ren'Py is open source:
http://www.renpy.org/

Tryano Builder is $15:
http://tyranobuilder.com/

Cheers!

Oh yes, one other thing with respect to Ren'Py, since it is open source and you will be hiring a programmer, if some of the basics of the engine seem to fit your needs but it is missing some features and some mods are required to really "make it your own", I guess it would probably be possible for the hired programmer to add the required functionality to the program while the engine has done most of the heavy lifting already.

Just a word of caution though, depending on how the program was coded and what sort of features you require, it may or may not be easier to modify and work within existing code than it is to use a different engine or to just program from scratch. If you do go the route of adding on to an open source project, you might want to show prospective programmers the source code and ask them if they think they can work with it efficiently or not.

I would recommend asking at the forum at intfiction.org. inform 7 and TADS 3 are the most powerful classical text adventure engines but illustrated games made with them are rare, and they require a lot of time to produce more than a small game. It would probably be much quicker to produce a high quality choose your own adventure book or visual novel. From what I remember a popular one is called Twine.

I don't have any input on a engine.

I loved choose your own adventure books as a kid. Couldn't get enough of them. My biggest pet peeve was when the book used the same ending for multiple paths. Sometime it makes sense but typically I felt gypped if I encountered the exact same ending multiple times. You knew it was was particularly bad when you learned to avoid a choice because you recognized the goto-page # for it. I recommend at least some degree of originality in the endings.

Best of luck with this!

the high res images are a non-negiotiable feature. cheers tho!
I doubt we'll end up there, but something worth remembering - cheers!
that always irked me as well. I guess its unavoidable to a degree - though - with it being a computer game (rather than a printed edition), there would be room to update things as time goes on a la Sunless Sea / Fallen London

Anybody mention Twine yet?

Colbert had a game Escape from the Man-Sized Cabinent made with Twine.

There are a buttload of choose your own adventure games on the Android, except that they don't really have recorded dialogue and VO and such.

I'm a big traditional fan of traditional gamebooks like Lone Wolf which has a full RPG system such as combat, abilities and loot. Not sure if that's overkill for what you're trying to do.

yeah, we're avoiding any kind of rpg system at all in favour of choices and content to allow the end user to explore the world / universe we set out without stat based boundaries.

Speaking of Fallen London, the system they use is available to work with, only downside being I think it's online only and largely based around the F2P style energy system (regenerates every hour or whatever) but might be worth a look.

There's a tool that might be useful to organize the story, its dialogue trees, characters and locations, as well as the artwork: <span class="bold">articy:draft 2</span>.  Nevigo also offers <span class="bold">articy:access</span>, a middleware library used to access articy:draft's projects from different platforms, including Unity.  According to Nevigo, CD Projekt uses articy:draft for the upcoming <span class="bold">Cyberpunk 2077</span>.  There's also <span class="bold">Dialogue System for Unity</span>, but articy:draft is intended for game designers and easier to use.


Useful videos:

 ▪  articy:draft 2: Official tutorials
 ▪  articy:draft 2: An overview
 ▪  Games designed with articy:draft
 ▪  Dialogue System for Unity - articy:draft Converter
 ▪  Dialogue Panel in Unity 5


Apparently, <span class="bold">Tin Man Games</span> uses Unity to create several Gamebook Adventures for the PC, iOS and Android.  Some of them are available on Steam:

   The Forest of Doom  ―  Curse of the Assassin  ―  An Assassin in Orlandes  ―  Starship Traveller  ― 
   Judge Dredd: Countdown Sector 106  ―  Caverns of the Snow Witch  ―  Appointment With FEAR

You bring up one good point: Unity is probably the way to go if you want to make sure you support multiple platforms like the "big 3" tablet OS'es. However, there are other "game makers" that do HTML type games -- which work on all platforms.

Construct 2 is one that comes to mind, but there is also GameMaker as well.

You might want to try . It's a free tool from inkle, who made the Sorcery! apps. They have [url=http://www.inklestudios.com/inklewriter/game-developers/]instructions on their site how to incorporate the result in a game. So it's not a direct conversion, but it may be a good tool for writing the story.

I haven't tried the tool but I played Sorcery! on Android and liked it quite a bit.

Other than Ren'Py which has already been mentioned, I want to give another left field option in RAGS. Not sure how well it will fit your needs, but it can make lovely stuff.