scheming
adj.making secret and dishonest plans to get what you want. You use this to describe someone who is tricky and cannot be trusted.
adj.involved in making secret, underhanded, or devious plans to achieve a personal goal. Often used to describe a person's character or a specific set of actions intended to deceive others.
“The scheming politician tried to trick his rivals.”
“After years of scheming to take over the family business, the eldest son was finally caught hiding the company's financial records.”
“The novel features a scheming antagonist whose elaborate plots are eventually undone by his own overconfidence and the loyalty of the protagonist's allies.”
Typically used as an attributive adjective before a noun, though it can follow linking verbs like 'be' or 'seem'.
“Today, fact and fantasy intermingle freely as a consequence of political scheming and jockeying for economic advantage.”
“Caitlin’s shrewish mother Janetta also thinks Frazer is the problem, and is forever scheming to separate him from Jamie.”
From scheme + -ing.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.