I often come when least expected, linking thoughts once unconnected. Before the plan or thing you do, I’m the first small spark breaking through.

My first is a number, my second another. And each, I assure you, will rhyme with the other. My first you will find is one-fifth of my second. And when added together, two dozen is reckoned.

If yet unmolested, then I mean to line. Bring me to an ER, your stock I'll confine. Hand me an L, the laments will come slow. Touch me to string, smaller pants I bestow.

Where ancient secrets still are unknown. For birds and eyes look back at the stone. Read me left or read me right, The Rosetta Stone brought me to light.

I can be part of your foot, yet I never wear a shoe. I stand above a grand doorway, yet I cannot see the view. I am the chief of villains, but I do no crime myself. I am a sneaky prefix sitting on a grammar shelf. What am I?