This is an add-on for The Battle For Wesnoth (www.wesnoth.org). It is currently only availabe on the stable branch, 1.12.6
Special thanks and image credits are in _main.cfg

Please comment at https://forums.wesnoth.org/viewtopic.php?f=31&t=43630

For lack of a better way to describe this mod, here is the description that's visible on the add-on server:

Year 891 YW. A series of raids on Wesnoth's Eastern flank is frighteningly reminiscent of the Eastern Invasion of 625. After the king dies in a failed counter-attack, Prince Reginald is left to save the kingdom. This time, however, Wesnoth cannot hope to withstand the undead invasion alone, so Reginald embarks on a desperate quest to gather allies. But as Lich Lord Malidron said himself, the Underworld is Rising...

Unlike my other add-ons, this one is extremely simple and perfectly follows the normal format for Wesnoth add-on campaigns.