Big Finish fills in the blanks about what happened when Moonbase Alpha encountered the planet Meta in their Space: 1999 episode, the Siren Call.  John and Eugene discuss

Episode Synopsis

Moonbase Alpha is still struggling in the aftermath of the events of Breakaway. A section decompression kills Alphan Mary Page. And it is in this moment we learn two things simultaneously – (1) that regular character Kano is married, and (2) Mary Page is her wife.  Actually, make that three things.  We also learn Kano is now widowed.  Oh, Mary Page, we hardly knew you.

Koenig is trying to hold a staff meeting, but Space Commissioner Simmonds, who is technically Koenig’s boss on the Org Chart is insisting on being “in charge.”  Koenig humors him by letting him lead the meeting, but it is Koenig who is clearly in command.  Simmonds wants them to find a way to travel 5 light years back to Earth.  Koenig and the others favor exploring their realistic options.  One of those options is the planet Meta, which the moon is approaching.  Meta was the source of the signal that resulted in the moon leaving Earth’s orbit via wormhole.

Before they can launch an exploration team, an emissary from the planet Pyrus arrives under the banner of peace.  Pyrus is the locals’ name for their own planet. Simmonds, talking on behalf of the Alphans greets Sazar, albeit with armed guards.  Simmonds favor the distrustful, show-of-force type of diplomacy.  

Sazar is the representative of Garadus, Pyrus’ leader.  Simmonds is so caught up in being the big man, he fails to find anything curious about the fact that Sazar speaks English, and he’s only a little curious when Koenig has Victor Bergman surreptitiously scan Sazar, only to discover that he is basically human, except that his heart isn’t beating.

While out of Simmonds earshot, Sazar meets with an Alphan who has been a spy for the Pyreans all along.  Between them, they engineer a scenario in which Sazar saves Simmonds’ life.  Sazar dies, but in his final selfless act, begins to earn Simmonds’ trust.

Garadus reaches out and invites them down to discuss the possibility of settling on the planet.  Koenig, Bergman, and Simmonds take an Eagle down.

On Alpha, Mary Page comes back to life and asks to be let out of the morgue.

On Pyrus, Koenig and Bergman remain suspicious, and when they get an inkling that the Meta Signal which drew them there may have been a lure, they sneak out to investigate. What they discover is macabre.  The basement is filled with cadavers on ice.

On Alpha, Mary Page turns out to be Sazar.  The Pyreans are non-corporeal being that inhabit corpses.  They have brought the Earth’s moon to Pyrus for a new supply of bodies.  Mary, an authorized engineer, sets about killing everyone on Alpha.  Helena, Kano, and Alan must stop her.

Simmonds overhears Garadus talking with Sazar and is taken for processing.  He overcomes his guard and escapes.  

Koenig and Bergman are also captured.  With Simmonds’ assistance, they escape back to their Eagle, but the Eagle has been disabled.  

In the nick of time, Paul Morrow arrives to take them home, and the Pyreans’ existing supply of bodies is destroyed by Koenig and Bergman’s mischief.