"I promise to bring the secret gadgets this time, instead of my grocery list." "I must not forget to charge my laser watch before leaving the headquarters." "Finally, we plan to escape through the bakery's back door if the villains find us."

Certain verbs, such as promise, forget (when talking about a task you must do), and plan, are followed by the to-infinitive (to + base verb). Using the gerund (-ing) or the bare infinitive without "to" is incorrect here.