in step
• putting one's feet forward alternately in the same rhythm as the people one is walking, marching, or dancing with.
• "the duo looked comfortable in each other's company, as well as walking in step with each other"
instep
noun
• the part of a person's foot between the ball and the ankle.
Origin:
late Middle English: of unknown origin; compare with West Frisian ynstap ‘opening in a shoe for insertion of the foot’.
