to guess the truth about a situation from pieces of information which you know about it.

I didn't tell her my husband had left, but she'd noticed his car was missing and put two and two together.

• straighten something out
• straighten up
• straighten up something
• straight-faced
• straight from the horse's mouth
• straight-from-the-shoulder
• straight from the shoulder
• straight shooter
• straight up
• strain every nerve
• strangely enough
• straw in the wind
• straw that breaks the camel's back
• street smarts
• stretch legs
• stretch the rules
• keep a weather eye on something
• keep body and soul together
• keep both feet on the ground
• keep cards close to chest
• keep cards close to your chest
• keep chin up
• keep close watch on
• keep close watch on someone
• keep close watch on something