How can I summon a willing target from elsewhere?

Question

I am the leader of my own crew of high-level characters. We have Necromancers, Brawlers, Assassins, Mind-Readers, etc. Because the world is always about to come to an end, they mostly wander in pairs going where they are needed.

However, I worry that an emergency may happen at headquarters, on such a scale, I'll need them all here immediately. Like, for example, last week, a Tarrasque decided to rampage nearby. That sort of emergency.

How can I arrange it?

I thought of mixing a Contingency with Teleport, but I cannot do that for others, and not all of them are high level spellcasters. Is there any way I can do this?

Let's assume preparation time is practically unlimited, as well as resources (we make thousands of gold per adventure, and just invest it in the realm). Also, I can probably hire strong casters from whatever class to cast or prepare spells for this (so no class requirements here). Any officially published materials are valid sources.

But once the system is in place, it needs to be able to be activated on as short notice as possible, for example by pressing a big button which may be in a fixed location at HQ.

Answer 1

The gate spell will do this

The gate spell says:

When you cast this spell, you can speak the name of a specific creature (a pseudonym, title, or nickname doesn't work). If that creature is on a plane other than the one you are on, the portal opens in the named creature's immediate vicinity and draws the creature through it to the nearest unoccupied space on your side of the portal.

So, step into an extraplanar space of your choice, then cast a series of gate spells off scrolls to pull your friends to you. Note that you only need one gate per group to be recalled, because the portal stays open after one character is pulled through.

If any of your friends are carrying bags of holding, you may wish to avoid pulling using a portable hole as your extraplanar space. The rope trick spell does not appear to be harmful to bags of holding, Rules As Written, which might make it a good choice. But it's still a good idea to check your DM's ruling before you decide what sort of extraplanar space to use.

Answer 2

Give them, or their friends, helms of teleportation.

This item lets you cast teleport without knowing any magic. You just need to magically communicate with them, and there's many ways to do that.

Answer 3

A Glyph of Warding with Word of Recall inside a Portable Hole.

So, the Portable Hole

creates an extradimensional hole 10 feet deep. The cylindrical space within the hole exists on a different plane, so it can't be used to create open passages. Any creature inside an open portable hole can exit the hole by climbing out of it.

A creature can enter and leave it when it wishes to. Then, you create a Glyph of Warding inside the Portable Hole. You can move the Portable Hole with you, since the Glyph isn't actually moving inside the extradimensional space.

You cast the Glyph of Warding at level 6 and create a Spell Glyph.

You can store a prepared spell of 3rd level or lower in the glyph by casting it as part of creating the glyph. The spell must target a single creature or an area. When the glyph is triggered, the stored spell is cast. If the spell has a target, it targets the creature that triggered the glyph. When you cast this spell using a spell slot of 4th level or higher, you can store any spell of up to the same level as the slot you use for the glyph of warding.

You now pick a spell that will target only you (even if the spell could affect more targets). We will take the Word of Recall. It's low level(-ish) and has no "you have to be in the same plane of existence" restrictions.

You and up to five willing creatures within 5 feet of you instantly teleport to a previously designated sanctuary.

Whoever activates the Glyph is instantly teleported to a predetermined shrine.

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If you don't have religious inclinations, use the Teleport spell instead. However, the glyph must be near the entrance of the Portable Hole, so that whoever activates it is in the Material Plane still, and is teleported to the target location. It also requires two level 7 spell slots.

PS: some people don't agree that these spells can be cast into a Glyph of Warding