One pandimensional entity from an ancient universe tried to "sneak" into N-Space via the Fourth Doctor's TARDIS's telepathic circuits. Collapsing the interior dimensions of his TARDIS, it tried to coordinate a ubiquitous attack on Earth.
However, the Doctor was warned of this by Sarah Jane Smith and activated the TARDIS tuner to contact his past and future incarnations through the TARDIS's telepathic circuits. After much bickering, a solution was worked out by the Sixth Doctor, who went back in time to the First Doctor's time in the TARDIS, installing a yellow button on the console which, when pressed by the other incarnations, flushed the entity out of the telepathic buffers. The War Doctor, in the meantime, had materialised his TARDIS at all the planned arrival points of the entity on Earth, stopping its invasion before it even began. (WC: Doctors Assemble!)