It's a Henrion, Dassy & Heuschen Revolver
I googled the "HDH" from your picture and came up with a number of different ones. They apparently were well known for making revolvers capable of firing many more rounds than 5 or 6. I didn't find that exact one, but there are several that have similar controls, etc.
This appears to be of the "bicycle gun" genre which were common but inexpensively made European firearms of the late 1800s-very early 1900s. The size, caliber, and folding trigger are what I base my guess on. Their purpose was for cyclists to use to fend off dogs as dogs seemed to dislike cyclists back then. One did not necessarily want to kill the dog, just scare it off, therefore the small calibers.
The value is something that I cannot guess at, I do not see them all that often and the company names have little meaning to me. I have bought some similar pistols as curiosities for under $100 and later sold them for much more to someone who really wanted them but have also seen some similar mogels at gunshows over and over for years at a lower asking price than what I got. I would suggest contacting Rock Island Auctions, they deal in a number of odd guns and may ber able to give you an estimate as to value.