Board Thread:Plants vs. Zombies 2/@comment-25083348-20151210192844/@comment-27557697-20151211122838

This is my guess for how Modern day will work. Now that everyone has two world keys....

Since I heard that there are going to be portals summoning zombies from other time periods... perhaps you can unlock modern day, but not progress to a level which contains a portal from a time period which you have not completed?