to begin doing something.

They set to work bringing order to an organization that didn't even know how many computers it had.

She pulled out her brushes and paper and set to work making a studio out of her hotel room.

• be in the throes of
• be in the throes of doing something
• be in the throes of something
• be in the wind
• be in the wrong
• be in too deep
• be in touch
• be in train
• be in two minds
• be in your blood
• be in your cups
• be in your element
• be in your face
• be joined at the hip
• be jolly hockey sticks
• be just a pretty face
• be just the job
• be just up someone's street
• be just up street
• be just what the doctor ordered
• be knee-deep in
• be knee-deep in something
• be knee-high to a grasshopper
• be larger than life
• be laughing all the way to the bank