So remember in the first Plants vs. Zombies when you randomly found a taco? Crazy Dave immediately bought it off of you for 1,000 coins, and then he pocketed the taco to eat later. Well in Plants vs. Zombies 2, Crazy Dave finally eats that taco. The taco is amazing. It's so delicious. It's the best thing that Dave has ever ate.
The taco is so good that he wants to time travel five minutes into the past to eat the taco all over again. So you and Dave hop into Penny, the talking time traveling car, and proceed to time travel into the past. Unfortunately, something goes wrong and so begins your adventure.