It might be
Tanacetum vulgare (Common Tansy). The red stem excludes many other plants with similar leaves.
One other possibility is Poison Hemlock, except that plant has stems that are more spotted with red blotches.
I'm really more inclined to think it's Tansy. JMO, though.

"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams