I understand that I need to own Starcraft 2: Wings of Liberty to play Heart of the Swarm, but I'm not sure where my disk is. If I can't find it, do I need to buy WoL again before I can play HotS?
If you purchased this disc version of Heart of the Swarm, it contains everything you need to play, you won't need to install Wings of Liberty first.
If you purchased the digital version, downloading HotS will also get you everything you need for WoL.
You do not need the disc, as you can download StarCraft 2: Wings of Liberty directly from the Battle.Net website:
- Log in with your Battle.Net account
- Choose the Account link in the top right
- In the "Your Game Accounts" list, find StarCraft 2
- Click the Starcraft 2: Wings of Liberty or StarCraft 2: Heart of the Swarm link to go to the Game Management Page
- From here you can download the Windows client. You can also select More Downloads to access the page with the Mac client download link.