What to call a "string with things attached"?

There are a number of idioms around the string, that carry the idea that if one pulls it, other things will (or will not) come with it:

with (no) strings attached

pulling strings

have the world on the string

string together

Conversely, is there an idiom to describe this metaphoric string (contract clause, pressure tactic, discovery) that leads to other things?

This clause in the contract is the --- that you should watch for.

This discovery is the --- that will lead to many other ones.

The golden thread.

Following the Golden thread

The golden thread is a symbol of the inspiration, intuition, and guiding light that graces us throughout our lives. It is that which we follow, knowing that it will, in some mysterious way, guide us on our true paths in life.

It is most colorfully portrayed in Greek mythology as the magical thread that Ariadne gave to Theseus, assisting him in his heroic journey into and out of the Minotaur's labyrinth. As we travel through literal and figurative labyrinths in our lives, the golden thread may easily go unnoticed, yet when it is recognized and followed, we may find that this archetypal strand of gold connects us to our true selves, to our beloveds, and to that which we discover to be home.

[Patrick Queen; Blogspot}

Operational planning is the “golden thread” linking strategy to execution and is ...

[Joe Evans_EvanCarmichael.com]