The Rules
Interrupt the action of the last card played. This card can be used at any time and can override a Stop card.
Tips & Tricks
A Halt card can be used to interrupt another Halt card.
FAQ
How does using Halt on a dwarf/item work does it still go into the play area?
You can interrupt the action of a dwarf or item card but only that card’s effect is interrupted; the card itself will still be placed in the play area and passive lasting effects will persist. For example if interrupted, Ragstad Iron Pumper will still be Immune to Gutter while Thrombold Ashenbeard will not have the Recruit effect.